Unusual neutral ligand coordination to arsenic and antimony trifluoride

The preparations and spectroscopic characterisation of the hydrolytically unstable As(III) complexes, [AsF(3)(OPR(3))(2)] (R = Me or Ph) and [AsF(3){Me(2)P(O)CH(2)P(O)Me(2)}] are described and represent the first examples of complexes of AsF(3) with neutral ligands. The crystal structure of [AsF(3){Me(2)P(O)CH(2)P(O)Me(2)}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at arsenic and producing a weakly associated polymer structure. The reaction of AsF(3) with OAsPh(3) affords Ph(3)AsF(2), and no arsine oxide complex was formed. Reaction of SbF(3) with OER(3) (R = Me or Ph, E = P or As), Me(2)P(O)CH(2)P(O)Me(2) and Ph(2)P(O)(CH(2))(n)P(O)Ph(2) (n = 1 or 2) in MeOH produces [SbF(3)(OER(3))(2)], [SbF(3){Me(2)P(O)CH(2)P(O)Me(2)}] and [SbF(3){Ph(2)P(O)(CH(2))(n)P(O)Ph(2)}] respectively. The X-ray structures reveal that the complexes contain square pyramidal SbF(3)O(2) cores with apical F and cis disposed pnictogen oxides. However, whilst [SbF(3)(OER(3))(2)] (R = Ph: E = P or As; R = Me: E = As) and [SbF(3){Ph(2)P(O)CH(2)P(O)Ph(2)}] are monomeric, [SbF(3){Me(2)P(O)CH(2)P(O)Me(2)}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF(3){Ph(2)P(O)(CH(2))(2)P(O)Ph(2)}] is a chain polymer with diphosphine dioxide bridges. In the OAsR(3) reactions with SbF(3), R(3)AsF(2) are also formed. Notably the Sb-O(P) bonds are shorter than As-O(P), despite the covalent radii (As < Sb), consistent with very weak coordination of the AsF(3). IR and multinuclear ((1)H, (19)F and (31)P) NMR data are reported and discussed. BiF(3) does not react with pnictogen oxide ligands under similar conditions and halide exchange of bismuth chloro complexes with Me(3)SnF gave BiF(3).     

Complexes of germanium(IV) fluoride with phosphane ligands: structural and spectroscopic authentication of germanium(IV) phosphane complexes

The first phosphane complexes of germanium(iv) fluoride, trans-[GeF(4)(PR(3))(2)] (R = Me or Ph) and cis-[GeF(4)(diphosphane)] (diphosphane = R(2)P(CH(2))(2)PR(2), R = Me, Et, Ph or Cy; o-C(6)H(4)(PR(2))(2), R = Me or Ph) have been prepared from [GeF(4)(MeCN)(2)] and the ligands in dry CH(2)Cl(2) and characterised by microanalysis, IR, Raman, (1)H, (19)F{(1)H} and (31)P{(1)H} NMR spectroscopy. The crystal structures of [GeF(4)(diphosphane)] (diphosphane = Ph(2)P(CH(2))(2)PPh(2) and o-C(6)H(4)(PMe(2))(2)) have been determined and show the expected cis octahedral geometries. In anhydrous CH(2)Cl(2) solution the complexes are slowly converted into the corresponding phosphane oxide adducts by dry O(2). The apparently contradictory literature on the reaction of GeCl(4) with phosphanes is clarified. The complexes trans-[GeCl(4)(AsR(3))(2)] (R = Me or Et) are obtained from GeCl(4) and AsR(3) either without solvent or in CH(2)Cl(2), and the structures of trans-[GeCl(4)(AsEt(3))(2)] and Et(3)AsCl(2) determined. Unexpectedly, the complexes of GeF(4) with arsane ligands are very unstable and have not been isolated in a pure state. The behaviour of the germanium(iv) halides towards phosphane and arsane ligands are compared with the corresponding silicon(iv) and tin(iv) systems.     

Diastereoselective proton transfer: a route to enantiomerically pure half-sandwich rhenium complexes

The diastereomeric methyl rhenium complex [CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)] was prepared in two steps from chiral racemic [CpRe(NO)(CO)(NCMe)]BF4 and the chiral racemic phosphine P(Me)(Ph)(2-C6H4NMe2). The unlike diastereomer reacts preferentially with MeSO3H to give the ring-closed ionic complex unlike-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 along with unreacted like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)], which is easily separated and converted to like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3. Starting from (R)-P(Me)(Ph)(2-C6H4NMe2), the diastereomerically and enantiomerically pure complexes (RRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 and (SRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 were obtained. Thus, this reaction sequence demonstrates a highly diastereoselective proton transfer from a functionalized chiral phosphine to a transition metal. Furthermore, it provides efficient access to enantiomerically pure half-sandwich rhenium complexes.     

Kinetic and mechanistic study of the Pt(II) versus Pt(IV) effect in the platinum-mediated nitrile-hydroxylamine coupling

The metal-mediated coupling between coordinated EtCN in the platinum(II) and platinum(IV) complexes cis- and trans-[PtCl(2)(EtCN)(2)], trans-[PtCl(4)(EtCN)(2)], a mixture of cis/trans-[PtCl(4)(EtCN)(2)] or [Ph(3)PCH(2)Ph][PtCl(n)(EtCN)] (n = 3, 5), and dialkyl- and dibenzylhydroxylamines R(2)NOH (R = Me, Et, CH(2)Ph, CH(2)C(6)H(4)Cl-p) proceeds smoothly in CH(2)Cl(2) at 20-25 degrees C and the subsequent workup allowed the isolation of new imino species [PtCl(n){NH=C(Et)ONR(2)}(2)] (n = 2, R = Me, cis-1 and trans-1; Et, cis-2 and trans-2; CH(2)Ph, cis-3 and trans-3; CH(2)C(6)H(4)Cl-p, cis-4 and trans-4; n = 4, R = Me, trans-9; Et, trans-10; CH(2)Ph, trans-11; CH(2)C(6)H(4)Cl-p, trans-12) or [Ph(3)PCH(2)Ph][PtCl(n){NH=C(Et)ONR(2)}] (n = 3, R = Me, 5; Et, 6; CH(2)Ph, 7; CH(2)C(6)H(4)Cl-p, 8; n = 5, R = Me, 13; Et, 14; CH(2)Ph, 15; CH(2)C(6)H(4)Cl-p, 16) in excellent to good (95-80%) isolated yields. The reduction of the Pt(IV) complexes 9-16 with the ylide Ph(3)P=CHCO(2)Me allows the synthesis of Pt(II) species 1-8. The compounds 1-16 were characterized by elemental analyses (C, H, N), FAB-MS, IR, (1)H, (13)C{(1)H}, and (31)P{(1)H} NMR (the latter for the anionic type complexes 5-8 and 13-16) and by X-ray crystallography for the Pt(II) (cis-1, cis-2, and trans-4) and Pt(IV) (15) species. Kinetic studies of addition of R(2)NOH (R = CH(2)C(6)H(4)Cl-p) to complexes [Ph(3)PCH(2)Ph][Pt(II)Cl(3)(EtCN)] and [Ph(3)PCH(2)Ph][Pt(IV)Cl(5)(EtCN)] by the (1)H NMR technique revealed that both reactions are first order in (p-ClC(6)H(4)CH(2))(2)NOH and Pt(II) or Pt(IV) complex, the second-order rate constant k(2) being three orders of magnitude larger for the Pt(IV) complex. The reactions are intermolecular in nature as proved by the independence of k(2) on the concentrations of added EtC triple bond N and Cl(-). These data and the calculated values of Delta H++ and Delta S++ are consistent with the mechanism involving the rate-limiting nucleophilic attack of the oxygen of (p-ClC(6)H(4)CH(2))(2)NOH at the sp-carbon of the C triple bond N bond followed by a fast proton migration.     

Amidoximes provide facile platinum(II)-mediated oxime-nitrile coupling

The nucleophilic addition of amidoximes R'C(NH(2))═NOH [R' = Me (2.Me), Ph (2.Ph)] to coordinated nitriles in the platinum(II) complexes trans-[PtCl(2)(RCN)(2)] [R = Et (1t.Et), Ph (1t.Ph), NMe(2) (1t.NMe(2))] and cis-[PtCl(2)(RCN)(2)] [R = Et (1c.Et), Ph (1c.Ph), NMe(2) (1c.NMe(2))] proceeds in a 1:1 molar ratio and leads to the monoaddition products trans-[PtCl(RCN){HN═C(R)ONC(R')NH(2)}]Cl [R = NMe(2); R' = Me ([3a]Cl), Ph ([3b]Cl)], cis-[PtCl(2){HN═C(R)ONC(R')NH(2)}] [R = NMe(2); R' = Me (4a), Ph (4b)], and trans/cis-[PtCl(2)(RCN){HN═C(R)ONC(R')NH(2)}] [R = Et; R' = Me (5a, 6a), Ph (5b, 6b); R = Ph; R' = Me (5c, 6c), Ph (5d, 6d), correspondingly]. If the nucleophilic addition proceeds in a 2:1 molar ratio, the reaction gives the bisaddition species trans/cis-[Pt{HN═C(R)ONC(R')NH(2)}(2)]Cl(2) [R = NMe(2); R' = Me ([7a]Cl(2), [8a]Cl(2)), Ph ([7b]Cl(2), [8b]Cl(2))] and trans/cis-[PtCl(2){HN═C(R)ONC(R')NH(2)}(2)] [R = Et; R' = Me (10a), Ph (9b, 10b); R = Ph; R' = Me (9c, 10c), Ph (9d, 10d), respectively]. The reaction of 1 equiv of the corresponding amidoxime and each of [3a]Cl, [3b]Cl, 5b-5d, and 6a-6d leads to [7a]Cl(2), [7b]Cl(2), 9b-9d, and 10a-10d. Open-chain bisaddition species 9b-9d and 10a-10d were transformed to corresponding chelated bisaddition complexes [7d](2+)-[7f](2+) and [8c](2+)-[8f](2+) by the addition of 2 equiv AgNO(3). All of the complexes synthesized bear nitrogen-bound O-iminoacylated amidoxime groups. The obtained complexes were characterized by elemental analyses, high-resolution ESI-MS, IR, and (1)H NMR techniques, while 4a, 4b, 5b, 6d, [7b](Cl)(2), [7d](SO(3)CF(3))(2), [8b](Cl)(2), [8f](NO(3))(2), 9b, and 10b were also characterized by single-crystal X-ray diffraction.     

Facile cyanamide-ammonia coupling mediated by cis- and trans-[PtIIL2] centers and giving metal-bound guanidines

Diffusion of ammonia into CH(2)Cl(2) solutions of the dialkylcyanamide complexes cis- or trans-[PtCl(2)(RCN)(2)] (R = NMe(2), NEt(2), NC(5)H(10)) at 20-25 degrees C leads to metal-mediated cyanamide-ammonia coupling to furnish, depending on reaction time, one or another type of novel bisguanidine compound, i.e. the molecular cis- or trans-[PtCl(2){NH=C(NH(2))R}(2)] (cis- and trans-) and the cationic cis- or trans-[Pt(NH(3))(2){NH=C(NH(2))R}(2)](Cl)(2) (cis- and trans-) complexes. Compounds cis- or trans- were converted to cis- or trans-, accordingly, upon prolonged treatment with NH(3) in CH(2)Cl(2). The ammination of the relevant nitrile complexes cis- or trans-[PtCl(2)(RCN)(2)] (R = Et, CH(2)Ph, Ph) in CH(2)Cl(2) solutions affords only the cationic compounds cis- or trans-[Pt(NH(3))(2){NH=C(NH(2))R}(2)](Cl)(2) (cis- and trans-). The formulation of was supported by satisfactory C, H and N elemental analyses, agreeable ESI(+)-MS (or FAB(+)-MS), IR, (1)H and (13)C NMR spectroscopies. The structures of trans-, trans-, cis-, trans-, cis-, and cis- were determined by single-crystal X-ray diffraction disclosing structural features and showing that the ammination gives ligated guanidines and amidines in the E- and Z-forms, respectively, where both correspond to the trans-addition of NH(3) to the nitrile species.     

Metal-promoted synthesis of amidines containing the model nucleobases 1-methylcytosine and 9-methyladenine

The amidine complexes cis-[L(2)PtNH==C(R){1-MeCy(-2H)}]NO(3) (R = Me, 1a; Ph, 1b, Me(3)C, 1c; Ph(2)(H)C, 1d) and cis-[L(2)PtNH==C(R){9-MeAd(-2H)}]NO(3) (R = Me, 2a; Ph, 2b; Me(3)C, 2c; Ph(2)(H)C, 2d), are formed when cis-[L(2)Pt(μ-OH)](2)(NO(3))(2) (L = PPh(3)) reacts with 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd) in solution of MeCN, PhCN, Me(3)CCN and Ph(2)(H)CCN. Reaction of 1a,b and 2a,b with HCl affords the protonated amidines [NH(2)==C(R){1-MeCy(-H)}]NO(3) (R = Me, 3a; Ph, 3b) and [NH(2)==C(R){9-MeAd(-H)}]NO(3) (R = Me, 4a; Ph, 4b) and cis-(PPh(3))(2)PtCl(2) in quantitative yield. Treatment of 3b and 4b with NaOH allows the isolation of the neutral benzimidamides NH(2)-C(Ph){1-MeCy(-2H)} (5b) and NH(2)-C(Ph){9-MeAd(-2H)} (6b). In the solid state 3b shows a planar structure with the hydrogen atom on N(4) cytosine position involved in a strong H-bond with the NO(3)(-) ion. Intermolecular H-bonds between the oxygen of the cytosine ring and one of the H atoms of the amidine-NH(2) group allow the dimerization of the molecule. A detailed analysis of the spectra of 3b in DMF-d(7) at -55 °C indicates the presence of an equilibrium between the species [NH(2)==C(R){1-MeCy(-H)}]NO(3) and [NH(2)==C(R){1-MeCy(-H)}](2)(NO(3))(2), exchanging with trace amounts of water at 25 °C. [(15)N,(1)H]-HMBC experiments for 5b and 6b indicate that the amino tautomer H(2)N-C(Ph){nucleobase(-2H)}, is the only detectable in solution and such structure has been confirmed in the solid state. The reaction of 5b and 6b with cis-L(2)Pt(ONO(2))(2) (L = PPh(3)), in chlorinated solvents, determines the immediate appearance of a pale yellow colour due to the coordination of the neutral amidine, likely in its imino form HN==C(Ph){nucleobase(-H)}, to give the adducts cis-[L(2)PtNH==C(Ph){nucleobase(-H)}](2+). In fact, addition of "proton sponge" leads to the immediate deprotonation of the amidine ligand with formation of the starting complexes 1b and 2b.     

Novel tailoring reaction for two adjacent coordinated nitriles giving platinum 1,3,5-triazapentadiene complexes

The tailoring reaction of the two adjacent nitrile ligands in cis-[PtCl(2)(RCN)(2)] (R = Me, Et, CH(2)Ph, Ph) and [Pt(tmeda)(EtCN)(2)][SO(3)CF(3)](2) (8.(OTf)(2); tmeda = N,N,N',N'-tetramethylethylenediamine) upon their interplay with N,N'-diphenylguanidine (DPG; NH=C(NHPh)(2)), in a 1:2 molar ratio gives the 1,3,5-triazapentadiene complexes [PtCl(2){NHC(R)NHC(R)=NH}] (1-4) and [Pt(tmeda){NHC(Et)NHC(Et)NH}][SO(3)CF(3)](2) (10.(OTf)(2)), respectively. In contrast to the reaction of 8.(OTf)(2) with NH=C(NHPh)(2), interaction of 8.(OTf)(2) with excess gaseous NH(3) leads to formation of the platinum(II) bis(amidine) complex cis-[Pt(tmeda){NH=C(NH(2))Et}(2)][SO(3)CF(3)](2) (9.(OTf)(2)). Treatment of trans-[PtCl(2)(RCN)(2)] (R = Et, CH(2)Ph, Ph) with 2 equiv of NH=C(NHPh)(2) in EtCN (R = Et) and CH(2)Cl(2) (R = CH(2)Ph, Ph) solutions at 20-25 degrees C leads to [PtCl{NH=C(R)NC(NHPh)=NPh}(RCN)] (11-13). When any of the trans-[PtCl(2)(RCN)(2)] (R = Et, CH(2)Ph, Ph) complexes reacts in the corresponding nitrile RCN with 4 equiv of DPG at prolonged reaction time (75 degrees C, 1-2 days), complexes containing two bidentate 1,3,5-triazapentadiene ligands, i.e. [Pt{NH=C(R)NC(NHPh)=NPh}(2)] (14-16), are formed. Complexes 14-16 exhibit strong phosphorescence in the solid state, with quantum yields (peak wavelengths) of 0.39 (530 nm), 0.61 (460 nm), and 0.74 (530 nm), respectively. The formulation of the obtained complexes was supported by satisfactory C, H, and N elemental analyses, in agreement with FAB-MS, ESI-MS, IR, and (1)H and (13)C{(1)H} NMR spectra. The structures of 1, 2, 4, 11, 13, 14, 9.(picrate)(2), and 10.(picrate)(2) were determined by single-crystal X-ray diffraction.     

Taking TiF4 complexes to extremes--the first examples with phosphine co-ligands

The first soft donor adducts of TiF(4), [TiF(4)(diphosphine)] (diphosphine = o-C(6)H(4)(PMe(2))(2), R(2)P(CH(2))(2)PR(2), R = Me or Et) have been prepared from [TiF(4)(MeCN)(2)] and the diphosphines in rigorously anhydrous CH(2)Cl(2), as extremely moisture sensitive yellow solids, and characterised by multinuclear NMR ((1)H, (31)P, (19)F), IR and UV/vis spectroscopy. The crystal structure of [TiF(4){Et(2)P(CH(2))(2)PEt(2)}] has been determined and shows a distorted six-coordinate geometry with disparate Ti-F(transF) and Ti-F(transP) distances and long Ti-P bonds. Weaker soft donor ligands including Ph(3)P, Ph(2)P(CH(2))(2)PPh(2), o-C(6)H(4)(PPh(2))(2), Ph(2)As(CH(2))(2)AsPh(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr do not form stable complexes with TiF(4), although surprisingly, fluorotitanate(IV) salts of the previously unknown doubly protonated ligand cations [LH(2)][Ti(4)F(18)] (L = o-C(6)H(4)(PPh(2))(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr) are formed in some cases as minor by-products. The structure of [o-C(6)H(4)(PPh(2)H)(2)][Ti(4)F(18)] shows the first authenticated example of a diprotonated o-phenylene-diphosphine. The synthesis and full spectroscopic characterisation are reported for a range of TiF(4) adducts with hard N- or O-donor ligands for comparison purposes, along with crystal structures of [TiF(4)(thf)(2)], [TiF(4)(Ph(3)EO)(2)]·2CH(2)Cl(2) (E = P or As), and [TiF(4)(bipy)].     

Si-H and Si-Si activation at Pt: synthesis and reactivity of neutral and cationic silyl complexes

Reactions of [Pt(PEt(3))(3)] (1) with the silanes HSiPh(3), HSiPh(2)Me and HSi(OEt)(3) led to the products of oxidative addition, cis-[Pt(H)(SiPh(3))(PEt(3))(2)] (2), cis-[Pt(H)(SiPh(2)Me)(PEt(3))(2)] (3), cis-[Pt(H){Si(OEt)(3)}(PEt(3))(2)] (cis-4) and trans-[Pt(H){Si(OEt)(3)}(PEt(3))(2)] (trans-4). The complexes cis-4 and trans-4 can also be generated by hydrogenolysis of (EtO)(3)SiSi(OEt)(3) in the presence of 1. Furthermore, the silyl compounds cis-4 and trans-4 react with B(C(6)F(5))(3) and CH(3)CN by hydride abstraction to give the cationic silyl complex trans-[Pt{Si(OEt)(3)}(NCCH(3))(PEt(3))(2)][HB(C(6)F(5))(3)] (8). In addition, the reactivity of the complexes cis-4, trans-4 and 8 towards alkenes and CO was studied using NMR experiments.     

Reactivity of niobium(v) and tantalum(v) halides with carbonyl compounds: synthesis of simple coordination adducts, C-H bond activation, C=O protonation, and halide transfer

The metal halides of Group 5 MX(5) (M = Nb, Ta; X = F, Cl, Br) react with ketones and acetylacetones affording the octahedral complexes [MX(5)(ketone)] () and [TaX(4){kappa(2)(O)-OC(Me)C(R)C(Me)O}] (R = H, Me, ), respectively. The adducts [MX(5)(acetone)] are still reactive towards acetone, acetophenone or benzophenone, giving the aldolate species [MX(4){kappa(2)(O)-OC(Me)CH(2)C(R)(R')O}] (). The syntheses of (M = Ta, X = F, R = R' = Ph) and (M = Ta, X = Cl, R = Me, R' = Ph) take place with concomitant formation of [(Ph(2)CO)(2)-H][TaF(6)], and [(MePhCO)(2)-H][TaCl(6)], respectively. The compounds [acacH(2)][TaF(6)], and [TaF{OC(Me)C(Me)C(Me)O}(3)][TaF(6)], have been isolated as by-products in the reactions of TaF(5) with acacH and 3-methyl-2,4-pentanedione, respectively. The molecular structures of, and have been ascertained by single crystal X-ray diffraction studies.     

Cationic diiron and diruthenium μ-allenyl complexes: synthesis, X-ray structures and cyclization reactions with ethyldiazoacetate/amine affording unprecedented butenolide- and furaniminium-substituted bridging carbene ligands

The novel cationic diiron μ-allenyl complexes [Fe(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe(2)Cp(2)(CO)(4)]. The solid state structures of [4a][CF(3)SO(3)] and of the diruthenium analogues [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}][BPh(4)] (R = Me, [2a][BPh(4)]; R = Ph, [2c][BPh(4)]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Br?nsted bases result in formation of the μ-allenylidene compound [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(1)-C(α)=C(β)=C(γ)(Ph)(2)}] (5) and of the dimetallacyclopentenone [Fe(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)=C(β)(C(γ)(Me)CH(2))C(=O)}] (6), respectively. The nitrile adducts [Ru(2)Cp(2)(CO)(NCMe)(μ-CO){μ-η(1):η(2)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a,c with MeCN/Me(3)NO, react with N(2)CHCO(2)Et/NEt(3) at room temperature, affording the butenolide-substituted carbene complexes [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(R)(2)OC(=O)C[upper bond 1 end](H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (9) has been detected in the course of the reaction leading to 10a. The addition of N(2)CHCO(2)Et/NHEt(2) to 7a gives the 2-furaniminium-carbene [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (11). The X-ray structures of 10a, 10b and [11][BF(4)] have been determined. The reactions of 4a,b with MeCN/Me(3)NO result in prevalent decomposition to mononuclear iron species.     

Bis(acetylacetonato)ruthenium(II) complexes containing alkynyldiphenylphosphines. Formation and redox behaviour of [Ru(acac)2(Ph2PC triple bond CR)2] (R=H, Me, Ph) complexes and the binuclear complex cis-[{Ru(acac)2}2(micro-Ph2PC triple bond CPPh2)}2

Two equivalents of Ph(2)PC triple bond CR (R=H, Me, Ph) react with thf solutions of cis-[Ru(acac)(2)(eta(2)-alkene)(2)] (acac=acetylacetonato; alkene=C(2)H(4), 1; C(8)H(14), 2) at room temperature to yield the orange, air-stable compounds trans-[Ru(acac)(2)(Ph(2)PC triple bond CR)(2)] (R=H, trans-3; Me=trans-4; Ph, trans-5) in isolated yields of 60-98%. In refluxing chlorobenzene, trans-4 and trans-5 are converted into the yellow, air-stable compounds cis-[Ru(acac)(2)(Ph(2)PC triple bond CR)(2)] (R=Me, cis-4; Ph, cis-5), isolated in yields of ca. 65%. From the reaction of two equivalents of Ph(2)PC triple bond CPPh(2) with a thf solution of 2 an almost insoluble orange solid is formed, which is believed to be trans-[Ru(acac)(2)(micro-Ph(2)PC triple bond CPPh(2))](n) (trans-6). In refluxing chlorobenzene, the latter forms the air-stable, yellow, binuclear compound cis-[{Ru(acac)(2)(micro-Ph(2)PC triple bond CPPh(2))}(2)] (cis-6). Electrochemical studies indicate that cis-4 and cis-5 are harder to oxidise by ca. 300 mV than the corresponding trans-isomers and harder to oxidise by 80-120 mV than cis-[Ru(acac)(2)L(2)] (L=PPh(3), PPh(2)Me). Electrochemical studies of cis-6 show two reversible Ru(II/III) oxidation processes separated by 300 mV, the estimated comproportionation constant (K(c)) for the equilibrium cis-6(2+) + cis6 <=> 2(cis-6(+)) being ca. 10(5). However, UV-Vis spectra of cis-6(+) and cis-6(2+), generated electrochemically at -50 degrees C, indicate that cis-6(+) is a Robin-Day Class II mixed-valence system. Addition of one equivalent of AgPF(6) to trans-3 and trans-4 forms the green air-stable complexes trans-3 x PF(6) and trans-4 x PF(6), respectively, almost quantitatively. The structures of trans-4, cis-4, trans-4 x PF(6) and cis-6 have been confirmed by X-ray crystallography.     

Synthesis and characterisation of mixed ligand Pt(II) and Pt(IV) oxadiazoline complexes

The nitrile ligands in trans-[PtX2(PhCN)2] (X = Cl, Br, I) undergo sequential 1,3 dipolar cycloadditions with nitrones R1R2C=N+(Me)-O(-) (R1 = H, R2 = Ph; R1 = CO2Et, R2 = CH2CO2Et) to selectively form the Delta4-1,2,4-oxadiazoline complexes trans-[PtX2(PhCN) (N=C(Ph)-O-N(Me)-CR1R2)] or trans-[PtX2(N=C(Ph)-O-N(Me)-CR1R2)2] in high yields. The reactivity of the mixed ligand complexes trans-[PtX2(PhCN)(N=C(Ph)-O-N(Me)-CR1R2)] towards oxidation and ligand substitution was studied in more detail. Oxidation with Cl2 or Br2 provides the Pt(IV) species trans-[PtX2Y2(PhCN)(N=C(Ph)-O-N(Me)-CH(Ph))] (X, Y = Cl, Br). The mixed halide complex (X = Cl, Y = Br) undergoes halide scrambling in solution to form trans-[PtX(4-n)Yn(PhCN)(N=C(Ph)-O-N(Me)-CH(Ph))] as a statistical mixture. Ligand substitution in trans-[PtCl2(PhCN)(N=C(Ph)-O-N(Me)-CR1R2)] allows for selective replacement of the coordinated nitrile by nitrogen heterocycles such as pyridine, DMAP or 1-benzyl-2-methylimidazole to produce mixed ligand Pt(II) complexes of the type trans- [PtX2(heterocycle)(N=C(Ph)-O-N(Me)-CR1R2)]. All compounds were characterised by elemental analysis, mass spectrometry, IR and 1H, 13C and 195Pt NMR spectroscopy. Single-crystal X-ray structural analysis of (R,S)-trans-[PtBr2(N=C(Ph)-O-N(Me)-CH(Ph))2] and trans-[PtCl2(C5H5N)(N=C(Ph)-O-N(Me)-CH(Ph))] confirms the molecular structure and the trans configuration of the heterocycles relative to each other.     

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(μ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(μ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(μ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.     

Hybrid dibismuthines and distibines as ligands towards transition metal carbonyls

The hybrid dibismuthines O(CH(2)CH(2)BiPh(2))(2) and MeN(CH(2)-2-C(6)H(4)BiPh(2))(2) react with [M(CO)(5)(thf)] (M = Cr or W) to form [{M(CO)(5)}(2){O(CH(2)CH(2)BiPh(2))(2)}] and [{Cr(CO)(5)}(2){MeN(CH(2)-2-C(6)H(4)BiPh(2))(2)}] containing bridging bidentate (Bi(2)) coordination. The unsymmetrical tertiary bismuthine complexes [M(CO)(5){BiPh(2)(o-C(6)H(4)OMe)}] are also described. Depending upon the molar ratio, the hybrid distibines O(CH(2)CH(2)SbMe(2))(2) and MeN(CH(2)-2-C(6)H(4)SbMe(2))(2) react with [M(CO)(5)(thf)] to give the pentacarbonyl complexes [{M(CO)(5)}(2){O(CH(2)CH(2)SbMe(2))(2)}] and [{Cr(CO)(5)}(2){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] or tetracarbonyls cis-[M(CO)(4){O(CH(2)CH(2)SbMe(2))(2)}] and cis-[M(CO)(4){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}]. The latter can also be obtained from [Cr(CO)(4)(nbd)] or [W(CO)(4)(pip)(2)], and contain chelating bidentates (Sb(2)-coordinated) as determined crystallographically. S(CH(2)-2-C(6)H(4)SbMe(2))(2) coordinates as a tridentate (SSb(2)) in fac-[M(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}] (M = Cr or Mo) and fac-[Mn(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)]. Fac-[Mn(CO)(3){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)] contains NSb(2)-coordinated ligand in the solid state, but in solution a second species, Sb(2)-coordinated and with a κ(1)-CF(3)SO(3) replacing the coordinated amine is also evident. X-ray crystal structures were also determined for fac-[Cr(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}], fac-[Mn(CO)(3){S(CH(2)-2-C(6)H(4)SbMe(2))(2)}][CF(3)SO(3)] and fac-[Mn(CO)(3){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] [CF(3)SO(3)]. Hypervalent N···Sb interactions are present in cis-[M(CO)(4){MeN(CH(2)-2-C(6)H(4)SbMe(2))(2)}] (M = Mo or W), but absent for M = Cr.     

Trapping unstable terminal M-O multiple bonds of monocyclopentadienyl niobium and tantalum complexes with Lewis acids

Hydrolysis of [NbCp'Cl(4)] (Cp' = η(5)-C(5)H(4)SiMe(3)) with the water adduct H(2)O·B(C(6)F(5))(3) afforded the oxo-borane compound [NbCp'Cl(2){O·B(C(6)F(5))(3)}] (2a). This compound reacted with [MgBz(2)(THF)(2)] giving [NbCp'Bz(2){O·B(C(6)F(5))(3)}] (2b), whereas [NbCp'Me(2){O·B(C(6)F(5))(3)}] (2c) was obtained from the reaction of [NbCp'Me(4)] with H(2)O·B(C(6)F(5))(3). Addition of Al(C(6)F(5))(3) to solutions containing the oxo-borane compounds [MCp(R)X(2){O·B(C(6)F(5))(3)}] (M = Ta, Cp(R) = η(5)-C(5)Me(5) (Cp*), X = Cl 1a, Bz 1b, Me 1c; M = Nb, Cp(R) = Cp', X = Cl 2a) afforded the oxo-alane complexes [MCp(R)X(2){O·Al(C(6)F(5))(3)}] (M = Ta, Cp(R) = Cp*, X = Cl 3a, Bz 3b, Me 3c; M = Nb, Cp(R) = Cp', X = Cl 4a), releasing B(C(6)F(5))(3). Compound 3a was also obtained by addition of Al(C(6)F(5))(3) to the dinuclear μ-oxo compound [TaCp*Cl(2)(μ-O)](2), meanwhile addition of the water adduct H(2)O·Al(C(6)F(5))(3) to [TaCp*Me(4)] gave complex 3c. The structure of 2a and 3a was obtained by X-ray diffraction studies. Density functional theory (DFT) calculations were carried out to further understand these types of oxo compounds.     

Direct addition of alcohols to organonitriles activated by ligation to a platinum(IV) center

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with R'OH (R' = Me, Et, n-Pr, i-Pr, n-Bu) at 45 degrees C in all cases allowed the isolation of the trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] imino ester complexes, while the reaction between cis-[PtCl(4)(RCN)(2)] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R/R' = Me/Me) or trans-[PtCl(4)[(E)-NH=C(Et)OR'](2)] (R' = Me, Et), the latter being formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction between alcohols R'OH and cis-[PtCl(4)(RCN)(2)] (R = Me, R' = Et, n-Pr, i-Pr, n-Bu; R = Et; R' = n-Pr, i-Pr, n-Bu), exhibiting greater R/R' steric congestion, allowed the isolation of cis-[PtCl(4)[(E)-NH=C(R)OR'][(Z)-NH=C(R)OR']] as the major products. The alcoholysis reactions of poorly soluble [PtCl(4)(RCN)(2)] (R = CH(2)Ph, Ph) performed under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R = Ph, with heating led to trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R = CH(2)Ph, R' = Me, Et, n-Pr, i-Pr; R = Ph, R' = Me) isolated in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R'OH to the organonitrile platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph(3)P=CHCO(2)Me, to the corresponding isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino ester ligands. Furthemore, the imino esters NH=C(R)OR' can be liberated from both platinum(IV) and platinum(II) complexes [PtCl(n)[H=C(R)OR'](2)] (n = 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine, respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass spectrometry, IR, and (1)H, (13)C[(1)H], and (195)Pt (metal complexes) NMR spectroscopies; the E and Z configurations of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray structure determinations were performed for trans-[PtCl(4)[(E)-NH=C(Me)OEt](2)] (2), trans-[PtCl(4)[(E)-NH=C(Et)OEt](2)] (10), trans-[PtCl(4)[(E)-NH=C(Et)OPr-i](2)] (11), trans-[PtCl(4)[(E)-NH=C(Et)OPr-n](2)] (12), and cis-[PtCl(4)[(E)-NH=C(Et)OMe](2)] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both platinum(II) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.     

The effect of micro-CN linkage isomerism and ancillary ligand set on directional metal-metal charge-transfer in cyanide-bridged dimanganese complexes

The reaction of [Mn(CN)L'(NO)(eta(5)-C(5)R(4)Me)] with cis- or trans-[MnBrL(CO)(2)(dppm)], in the presence of Tl[PF(6)], gives homobinuclear cyanomanganese(i) complexes cis- or trans-[(dppm)(CO)(2)LMn(micro-NC)MnL'(NO)(eta(5)-C(5)R(4)Me)](+), linkage isomers of which, cis- or trans-[(dppm)(CO)(2)LMn(micro-CN)MnL'(NO)(eta(5)-C(5)R(4)Me)](+), are synthesised by reacting cis- or trans-[Mn(CN)L(CO)(2)(dppm)] with [MnIL'(NO)(eta(5)-C(5)R(4)Me)] in the presence of Tl[PF(6)]. X-Ray structural studies on the isomers trans-[(dppm)(CO)(2){(EtO)(3)P}Mn(micro-NC)Mn(CNBu(t))(NO)(eta(5)-C(5)H(4)Me)](+) and trans-[(dppm)(CO)(2){(EtO)(3)P}Mn(micro-CN)Mn(CNBu(t))(NO)(eta(5)-C(5)H(4)Me)](+) show nearly identical molecular structures whereas cis-[(dppm)(CO)(2){(PhO)(3)P}Mn(micro-NC)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me)](+) and cis-[(dppm)(CO)(2){(PhO)(3)P}Mn(micro-CN)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me)](+) differ, effectively in the N- and C-coordination respectively of two different optical isomers of the pseudo-tetrahedral units (NC)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me) and (CN)Mn{P(OPh)(3)}(NO)(eta(5)-C(5)H(4)Me) to the octahedral manganese centre. Electrochemical and spectroscopic studies on [(dppm)(CO)(2)LMn(micro-XY)MnL'(NO)(eta(5)-C(5)R(4)Me)](+) show that systematic variation of the ligands L and L', of the cyclopentadienyl ring substituents R, and of the micro-CN orientation (XY = CN or NC) allows control of the order of oxidation of the two metal centres and hence the direction and energy of metal-metal charge-transfer (MMCT) through the cyanide bridge in the mixed-valence dications. Chemical one-electron oxidation of cis- or trans-[(dppm)(CO)(2)LMn(micro-NC)MnL'(NO)(eta(5)-C(5)R(4)Me)](+) with [NO][PF(6)] gives the mixed-valence dications trans-[(dppm)(CO)(2)LMn(II)(micro-NC)Mn(I)L'(NO)(eta(5)-C(5)R(4)Me)](2+) which show solvatochromic absorptions in the electronic spectrum, assigned to optically induced Mn(I)-to-Mn(II) electron transfer via the cyanide bridge.     

New insights into the polymerization of methyl methacrylate initiated by rare-earth borohydride complexes: a combined experimental and computational approach

Polymerization of methyl methacrylate (MMA) initiated by the rare-earth borohydride complexes [Ln(BH(4))(3)(thf)(3)] (Ln=Nd, Sm) or [Sm(BH(4))(Cp*)(2)(thf)] (Cp*=eta-C(5)Me(5)) proceeds at ambient temperature to give rather syndiotactic poly(methyl methacrylate) (PMMA) with molar masses M(n) higher than expected and quite broad molar mass distributions, which is consistent with a poor initiation efficiency. The polymerization of MMA was investigated by performing density functional theory (DFT) calculations on an eta-C(5)H(5) model metallocene and showed that in the reaction of [Eu(BH(4))(Cp)(2)] with MMA the borate [Eu(Cp)(2){(OBH(3))(OMe)C=C(Me)(2)}] (e-2) complex, which forms via the enolate [Eu(Cp)(2){O(OMe)C=C(Me)(2)}] (e), is calculated to be exergonic and is the most likely of all of the possible products. This product is favored because the reaction that leads to the formation of carboxylate [Eu(Cp)(2){OOC-C(Me)(=CH(2))}] (f) is thermodynamically favorable, but kinetically disfavored, and both of the potential products from a Markovnikov [Eu(Cp)(2){O(OMe)C-CH(Me)(CH(2)BH(3))}] (g) or anti-Markovnikov [Eu(Cp)(2){O(OMe)C-C(Me(2))(BH(3))}] (h) hydroboration reaction are also kinetically inaccessible. Similar computational results were obtained for the reaction of [Eu(BH(4))(3)] and MMA with all of the products showing extra stabilization. The DFT calculations performed by using [Eu(Cp)(2)(H)] to model the mechanism previously reported for the polymerization of MMA initiated by [Sm(Cp*)(2)(H)](2) confirmed the favorable exergonic formation of the intermediate [Eu(Cp)(2){O(OMe)C=C(Me)(2)}] (e') as the kinetic product, this enolate species ultimately leads to the formation of PMMA as experimentally observed. Replacing H by BH(4) thus prevents the 1,4-addition of the [Eu(BH(4))(Cp)(2)] borohydride ligand to the first incoming MMA molecule and instead favors the formation of the borate complex e-2. This intermediate is the somewhat active species in the polymerization of MMA initiated by the borohydride precursors [Ln(BH(4))(3)(thf)(3)] or [Sm(BH(4))(Cp*)(2)(thf)].