Stereospecific synthesis of polysubstituted E-olefins by reaction of acyclic nitrones with free and platinum(II) coordinated organonitriles

Free nitriles NCCH2R (1a R = CO2Me, 1b R = SO2Ph, and 1c R = COPh) with an acidic alpha-methylene react with acyclic nitrones -O+N(Me)=C(H)R' (2a R' = 4-MeC6H4 and 2b R' = 2,4,6-Me3C6H2), in refluxing CH2Cl2, to afford stereoselectively the E-olefins (NC)(R)C=C(H)R' (3a-3c and 3a'-3c'), whereas, when coordinated at the platinum(II) trans-[PtCl2(NCCH2R)2] complexes (4a R = CO2Me and 4b R = Cl), they undergo cycloaddition to give the (oxadiazoline)-PtII complexes trans-[PtCl2{N=C(CH2R)ON(Me)C(H)R'}2] (R = CO2Me, Cl and R' = 4-MeC6H4, 2,4,6-Me3C6H2) (5a-5d). Upon heating in CH2Cl2, 5a affords the corresponding alkene 3a. The reactions are greatly accelerated when carried out under focused microwave irradiation, particularly in the solid phase (SiO2), without solvent, a substantial increase of the yields being also observed. The compounds were characterized by IR and 1H, 13C, and 195Pt NMR spectroscopies, FAB+-MS, elemental analyses and, in the cases of the alkene (NC)(CO2Me)C=C(H)(4-MeC6H4) 3a and of the oxadiazoline complex trans-[PtCl2{N=C(CH2Cl)ON(Me)C(H)(4-C6H4Me)}2] 5c, also by X-ray diffraction analyses.     

Phosphorus copies of PPV: pi-conjugated polymers and molecules composed of alternating phenylene and phosphaalkene moieties

A new class of pi-conjugated macromolecule, poly(p-phenylenephosphaalkene) (PPP), is reported. PPPs are phosphorus analogues of the important electronic material poly(p-phenylenevinylene) (PPV) where P=C rather than C=C bonds space phenylene moieties. Specifically, PPPs [-C(6)R(4)-P=C(OSiMe(3))-C(6)R'(4)-C(OSiMe(3))=P-](n)() (1: R = H, R' = Me; 11: R = Me, R' = H) were synthesized by utilizing the Becker reaction of a bifunctional silylphosphine, 1,4-C(6)R(4)[P(SiMe(3))(2)](2), and diacid chloride 1,4-C(6)R'(4)[COCl](2). Several model compounds for PPP are reported. Namely, mono(phosphaalkene)s R-P=C(OSiMe(3))-R' (4: R = Ph, R' = Mes; 7: R = Mes, R' = Ph), C-centered bis(phosphaalkene)s R-P=C(OSiMe(3))-C(6)R'(4)-C(OSiMe(3))=P-R (5: R = Ph, R' = Me; 8: R = Mes, R' = H), and P-centered bis(phosphaalkene)s R-C(OSiMe(3))=P-C(6)R'(4)-P=C(OSiMe(3))-R (6: R = Mes, R' = H; 10: R = Ph, R' = Me). Remarkably, selective Z-isomer formation (i.e., trans arylene moieties) is observed for PPPs when bulky P-substituents are employed while E/Z-mixtures are otherwise obtained. X-ray crystal structures of Z-7, Z,Z-8, and Z,Z-10 suggest moderate pi-conjugation. The twist angles between the P=C plane and unsubstituted arenes are 16 degrees -26 degrees , while those between the P=C plane and methyl-substituted arenes are 59 degrees -67 degrees . The colored PPPs and their model compounds were studied by UV/vis spectroscopy, and the results are consistent with extended pi-conjugation. Specifically, weakly emissive polymer E/Z-1 (lambda(max) = 338 nm) shows a red shift in its absorbance from model E/Z-4 (lambda(max) = 310 nm), while a much larger red shift is observed for Z-11 (lambda(max) = 394 nm) over Z-7 (lambda(max) = 324 nm).     

Interaction of tertiary phosphines with lignin-type, alpha,beta-unsaturated aldehydes in water

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, lignin chromophores, such as the alpha,beta-unsaturated aromatic aldehydes, sinapaldehyde, coniferylaldehyde, and coumaraldehyde, were reacted with the tertiary phosphines R2R'P [R = R' = Me, Et, (CH2)3OH, iPr, cyclo-C6H11, (CH2)2CN; R = Me or Et, R' = Ph; R = Ph, R' = Me, m-NaSO3-C6H4] in water at room temperature under argon. In all cases, initial nucleophilic attack of the phosphine occurs at the activated C=C bond to form a zwitterionic monophosphonium species. With the phosphines PR3 [R = Me, Et, (CH2)3OH] and with R2R'P (R = Me or Et, R' = Ph), the zwitterion undergoes self-condensation to give a bisphosphonium zwitterion that can react with aqueous HCl to form the corresponding dichloride salts (as a mixture of R,R- and S,S-enantiomers); X-ray structures are presented for the bisphosphonium chlorides synthesized from the Et3P and Me3P reactions with sinapaldehyde. With the more bulky phosphines, iPr3P, MePPh2, (cyclo-C6H11)3P, and Na[Ph2P(m-SO3-C6H4)], only an equilibrium of the monophosphonium zwitterion with the reactant aldehyde is observed. The weakly nucleophilic [NC(CH2)2]3P does not react with sinapaldehyde. An analysis of some exceptional 1H NMR data within the prochiral phosphorus centers of the bisphosphonium chlorides is also presented.     

Substituent effects on Ni-S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis(phosphinite)-based pincer ligand

Pincer complexes of the type [2,6-(R(2)PO)(2)C(6)H(3)]NiSC(6)H(4)Z (R = Ph and i-Pr; Z = p-OCH(3), p-CH(3), H, p-Cl, and p-CF(3)) have been synthesized from [2,6-(R(2)PO)(2)C(6)H(3)]NiCl and sodium arylthiolate. X-ray structure determinations of these thiolate complexes have shown a somewhat constant Ni-S bond length (approx. 2.20 ?) but an almost unpredictable orientation of the thiolate ligand. Equilibrium constants for various thiolate exchange (between a nickel thiolate complex and a free thiol, or between two different nickel thiolate complexes) reactions have been measured. Evidently, the thiolate ligand with an electron-withdrawing substituent prefers to bond with "[2,6-(Ph(2)PO)(2)C(6)H(3)]Ni" rather than "[2,6-(i-Pr(2)PO)(2)C(6)H(3)]Ni", and bonds least favourably with hydrogen. The reactions of the thiolate complexes with halogenated compounds such as PhCH(2)Br, CH(3)I, CCl(4), and Ph(3)CCl have been examined and several mechanistic pathways have been explored.     

Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

Paramagnetic CpCr(III) complexes with antiferromagnetically-coupled anionic radical diimine and pyridine-imine ligands were prepared and characterized. The diimine chloro CpCr[(ArNCR)(2)]Cl complexes (1: Ar = 2,6-iPr(2)C(6)H(3) (Dpp), R = H; 2: Ar = 2,6-Me(2)C(6)H(3) (Xyl), R = Me; 3: Ar = 2,4,6-Me(3)C(6)H(2) (Mes), R = Me) were synthesized by treatment of previously reported Cr(diimine)(THF)(2)Cl(2) precursors with NaCp. Reduction of 1 with Zn gives CpCr[(DppNCH)(2)], 4, resulting from reduction of Cr(III) to Cr(II) with retention of the ligand-based radical. Alkoxide complexes CpCr[(DppNCH)(2)](OCR(2)R') (5: R = Me, R' = Ph; 6: R = iPr, R' = H) were synthesized by protonolysis of Cp(2)Cr with HOCR(2)R' in the presence of the neutral diimine and catalytic base. The corresponding radical pyridine-imine complexes CpCr(PyCHNMes)Cl (9), CpCr(PyCHNMes) (8), and CpCr(PyCHNMes)(OCMe(2)Ph) (11), were prepared by analogous routes. Oxidation of 8 with iodine gives CpCr(PyCHNMes)I (10) where oxidation of Cr(II) to Cr(III) again occurs with retention of the anionic pyridine-imine radical ligand. The molecular structures of complexes 1, 2, 4-8, 10 and 11 were determined by single-crystal X-ray diffraction. Unusual low energy bands were observed in the UV-vis spectra of the reported complexes, with particularly strong transitions observed for the Cr(II) complexes 4 and 8. The electronic structure of pyridine-imine complexes 8 and 10 were investigated by theoretical calculations.     

Beta-diiminate platinum complexes for alkane dehydrogenation

New five-coordinate Pt(IV) complexes [{(o-R2-p-R'-C6H2)NC(R' ')}2CH]PtMe3 (R, R', R' ' = alkyl or H) are reported. The complex with R = Me, R' = tBu, R' ' = Me generates unsaturated Pt(II) species capable of alkane C-H bond activation and stoichiometric dehydrogenation.     

A Route to 1,2,4-oxadiazoles and their complexes via platinum-mediated 1,3-dipolar cycloaddition of nitrile oxides to organonitriles

A significant activation of the Ctbd1;N group in organonitriles upon their coordination to a platinum(IV) center has been found in the reaction of [PtCl(4)(RCN)(2)] (R = Me, Et, CH(2)Ph) with the nitrile oxides 2,4,6-R'(3)C(6)H(2)CNO (R' = Me, OMe) to give the (1,2,4-oxadiazole)platinum(IV) complexes (R = Me, R' = Me (1); R = Et, R' = Me (2); R = Et, R' = OMe (3); R = CH(2)Ph, R' = Me (4)); the [2 + 3] cycloaddition was performed under mild conditions (unless poor solubility of [PtCl(4)(RCN)(2)] precludes the reaction) starting even from complexed acetonitrile and propionitrile, which exhibit low reactivity in the free state. The reaction between complexes 2-4 and 1 equiv of Ph(3)P=CHCO(2)Me in CH(2)Cl(2) leads to the appropriate platinum(II) complexes (5-7); the reduction failed only in the case of 1 insofar as this complex is insoluble in the most common organic solvents. All the platinum compounds were characterized by elemental analyses, FAB mass spectrometry, and IR and (1)H, (13)C((1)H), and (195)Pt NMR spectroscopies, and three of them also by X-ray crystallography. The oxadiazoles formed in the course of the metal-mediated reaction were liberated almost quantitatively from their Pt(IV) complexes by reaction of the latter (complexes 2-4) with an excess of pyridine in chloroform, giving free 1,2,4-oxadiazoles and trans-[PtCl(4)(pyridine)(2)]; the sequence of the Pt(IV)-mediated [2 + 3] cycloaddition and the liberation opens up an alternative route for the preparation of this important class of heterocycles.     

Catalytic addition of amine N-H bonds to carbodiimides by half-sandwich rare-earth metal complexes: efficient synthesis of substituted guanidines through amine protonolysis of rare-earth metal guanidinates

Reaction of [Ln(CH(2)SiMe(3))(3)(thf)(2)] (Ln=Y, Yb, and Lu) with one equivalent of Me(2)Si(C(5)Me(4)H)NHR' (R'=Ph, 2,4,6-Me(3)C(6)H(2), tBu) affords straightforwardly the corresponding half-sandwich rare-earth metal alkyl complexes [{Me(2)Si(C(5)Me(4))(NR')}Ln(CH(2)SiMe(3))(thf)(n)] (1: Ln = Y, R' = Ph, n=2; 2: Ln = Y, R' = C(6)H(2)Me(3)-2,4,6, n=1; 3: Ln = Y, R' = tBu, n=1; 4: Ln = Yb, R' = Ph, n=2; 5: Ln = Lu, R' = Ph, n=2) in high yields. These complexes, especially the yttrium complexes 1-3, serve as excellent catalyst precursors for the catalytic addition of various primary and secondary amines to carbodiimides, efficiently yielding a series of guanidine derivatives with a wide range of substituents on the nitrogen atoms. Functional groups such as C[triple chemical bond]N, C[triple chemical bond]CH, and aromatic C--X (X: F, Cl, Br, I) bonds can survive the catalytic reaction conditions. A primary amino group can be distinguished from a secondary one by the catalyst system, and therefore, the reaction of 1,2,3,4-tetrahydro-5-aminoisoquinoline with iPrN==C==NiPr can be achieved stepwise first at the primary amino group to selectively give the monoguanidine 38, and then at the cyclic secondary amino unit to give the biguanidine 39. Some key reaction intermediates or true catalyst species, such as the amido complexes [{Me(2)Si(C(5)Me(4))(NPh)}Y(NEt(2))(thf)(2)] (40) and [{Me(2)Si(C(5)Me(4))(NPh)}Y(NHC(6)H(4)Br-4)(thf)(2)] (42), and the guanidinate complexes [{Me(2)Si(C(5)Me(4))(NPh)}Y{iPrNC(NEt(2))(NiPr)}(thf)] (41) and [{Me(2)Si(C(5)Me(4))(NPh)}Y{iPrN}C(NC(6)H(4)Br-4)(NHiPr)}(thf)] (44) have been isolated and structurally characterized. Reactivity studies on these complexes suggest that the present catalytic formation of a guanidine compound proceeds mechanistically through nucleophilic addition of an amido species, formed by acid-base reaction between a rare-earth metal alkyl bond and an amine N--H bond, to a carbodiimide, followed by amine protonolysis of the resultant guanidinate species.     

Lithium aluminates on a molecular titanium oxide

Lithium aluminates Li[Al(O-2,6-Me(2)C(6)H(3))R'(3)] (R' = Et, Ph) react with the μ(3)-alkylidyne oxoderivative ligands [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] to afford the aluminum-lithium-titanium cubane complexes [{R'(3)Al(μ-O-2,6-Me(2)C(6)H(3))Li}(μ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(μ(3)-CR)] [R = H, R' = Et (5), Ph (7); R = Me, R' = Et (6), Ph (8)]. Complex 7 evolves with the formation of a lithium dicubane species and a Li{Al(μ-O-2,6-Me(2)C(6)H(3))Ph(3)}(2)] unit.     

Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes

The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.     

Different C-C coupling reactions of permethyltitanocene and permethylzirconocene with disubstituted 1,3-butadiynes

Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-]] (3), containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). When using the analogous permethyltitanocene fragment "Cp2*Ti", the reaction depends strongly on the substituents R and R'. The coupling product of the butadiyne with two methyl groups of one of the pentamethylcyclopentadienyl ring systems, [Cp*Ti[eta5-C5Me3-(CH2-CHR-eta2-C2-CHR'-CH2)]], is obtained with R = R' = tBu (4) and R = tBu, R' = SiMe3 (5). In these complexes one pentamethylcyclopentadienyl ligand is annellated to an eight-membered ring with a C-C triple bond, which is coordinated to the titanium center. A different activation of both pentamethylcyclopentadienyl ligands is observed for R = R' = Me, resulting in the complex [[eta5-C5Me4(CH2)-]Ti[-C(=CHMe)-C(=CHMe)-CH2-eta5-C5Me4]] (6), which displays a fulvene as well as a butadienyl-substituted pentamethylcyclopentadienyl ligand. The influence exerted by the size of the metal is illustrated in the reaction of [Cp2*ZrCl2] with MeC triple bond C-C triple bond CMe. Here the five-membered metallacyclocumulene complex [Cp2*Zr(eta4-1,2,3,4-MeC4Me)] (7) is obtained. The reaction paths found for R = R' = Me are identical to those formerly described for R = R' = Ph.     

Early/Late Heteronuclear Complexes Bridged by Bifunctional Phosphorus-Based Ligands

Substituted bifunctional phosphorus-based ligands HX(CRR') n PR"H (or -PR" 2 ) [where X = O, S, NR', (substituted) cyclopentadienyl; n = 1, 2, 3; R, R', R" = alkyl, aryl, H] were employed as bridging ligands in the synthesis of early/late bridged transition metal complexes. Synthetic routes to the bifunctional ligands were also developed. First, mononuclear complexes, such as [TpZr(OCH 2 PPh 2 ) 3 ] (Tp = trispyrazolylborato), [Cp 2 Zr(1-O-2-PHR-C 6 H 10 )(Me)] (R = 2,4,6-Pr i 3 C 6 H 2 (Tipp)), [Cp 2 Zr(SCH 2 CH 2 PHR) 2 ] (R = Ph, Mes, Tipp), and phosphinoferrocene derivatives, were prepared. These complexes are suitable precursors for the introduction of a second metal (as in, for example, [TpZr( w -OCH 2 PPh 2 ) 3 Mo(CO) 3 ]).     

Substituent effects on indium-phosphorus bonding in (4-RC6H4S)3In.PR'3 adducts (R = H, Me, F; R' = Et, Cy, Ph): a spectroscopic, structural, and thermal decomposition study

The tris(arylthiolate)indium(III) complexes (4-RC(6)H(4)S)(3)In [R = H (5), Me (6), F (7)] were prepared from the 2:3 reaction of elemental indium and the corresponding aryl disulfide in methanol. Reaction of 5-7 with 2 equiv of the appropriate triorganylphosphine in benzene or toluene resulted in isolation of the indium-phosphine adduct series (4-RC(6)H(4)S)(3)In.PR'(3) [R = H, R' = Et (5a), Cy (5b), Ph (5c); R = Me, R' = Et (6a), Cy (6b), Ph (6c); R = F, R' = Et (7a), Cy (7b), Ph (7c)]. These compounds were characterized via elemental analysis, FT-IR, FT-Raman, solution (1)H, (13)C{(1)H}, (31)P{(1)H}, and (19)F (7a-c) NMR spectroscopy, and X-ray crystallography (5c, 6a, 6c, and 7a). NMR spectra show retention of the In-P bond in benzene-d(6) solution, with phosphine (31)P{(1)H} signals shifted downfield compared to the uncoordinated ligand. The X-ray structures show monomeric 1:1 adduct complexes in all cases. The In-P bond distance [2.5863(5)-2.6493(12) A] is influenced significantly by the phosphine substituents but is unaffected by the substituted phenylthiolate ligand. Relatively low melting points (88-130 degrees C) are observed for all adducts, while high-temperature thermal decomposition is observed for the indium thiolate reactants 5-7. DSC/TGA and EI-MS data show a two-step thermal decomposition process, involving an initial loss of the phosphine moiety followed by loss of thiolate ligand.     

Synthesis and reactivity of calix[4]arene-supported group 4 imido complexes

New mononuclear titanium and zirconium imido complexes [M(NR)(R'(2)calix)] [M=Ti, R'=Me, R=tBu (1), R=2,6-C(6)H(3)Me(2) (2), R=2,6-C(6)H(3)iPr(2) (3), R=2,4,6-C(6)H(2)Me(3) (4); M=Ti, R'=Bz, R=tBu (5), R=2,6-C(6)H(3)Me(2) (6), R=2,6-C(6)H(3)iPr(2) (7); M=Zr, R'=Me, R=2,6-C(6)H(3)iPr(2) (8)] supported by 1,3-diorganyl ether p-tert-butylcalix[4]arenes (R'(2)calix) were prepared in good yield from the readily available complexes [MCl(2)(Me(2)calix)], [Ti(NR)Cl(2)(py)(3)], and [Ti(NR)Cl(2)(NHMe(2))(2)]. The crystallographically characterised complex [Ti(NtBu)(Me(2)calix)] (1) reacts readily with CO(2), CS(2), and p-tolyl-isocyanate to give the isolated complexes [Ti[N(tBu)C(O)O](Me(2)calix)] (10), [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [Ti[N(tBu)C(O)N(-4-C(6)H(4)Me)](Me(2)calix)] (13). In the case of CO(2) and CS(2), the addition of the heterocumulene to the Ti-N multiple bond is followed by a cycloreversion reaction to give the dinuclear complexes 11 and 12. The X-ray structure of 13.4(C(7)H(8)) clearly establishes the N,N'-coordination mode of the ureate ligand in this compound. Complex 1 undergoes tert-butyl/arylamine exchange reactions to form 2, 3, [Ti(N-4-C(6)H(4)Me)(Me(2)calix)] (14), [Ti(N-4-C(6)H(4)Fc)(Me(2)calix)] (15) [Fc=Fe(eta(5)-C(5)H(5))(eta(5)-C(5)H(4))], and [[Ti(Me(2)calix)](2)[mu-(N-4-C(6)H(4))(2)CH(2)]] (16). Reaction of 1 with H(2)O, H(2)S and HCl afforded the compounds [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [TiCl(2)(Me(2)calix)] in excellent yields. Furthermore, treatment of 1 with two equivalents of phenols results in the formation of [Ti(O-4-C(6)H(4)R)(2)(Me(2)calix)] (R=Me 17 or tBu 18), [Ti(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (19) and [Ti(mbmp)(Me(2)calix)] (20; H(2)mbmp=2,2'-methylene-bis(4-methyl-6-tert-butylphenol) or CH(2)([CH(3)][C(4)H(9)]C(6)H(2)-OH)(2)). The bis(phenolate) compounds 17 and 18 with para-substituted phenolate ligands undergo elimination and/or rearrangement reactions in the nonpolar solvents pentane or hexane. The metal-containing products of the elimination reactions are dinuclear complexes [[Ti(O-4-C(6)H(4)R)(Mecalix)](2)] [R=Me (23) or tBu (24)] where Mecalix=monomethyl ether of p-tert-butylcalix[4]arene. The products of the rearrangement reaction are [Ti(O-4-C(6)H(4)Me)(2) (paco-Me(2)calix)] (25) and [Ti(O-4-C(6)H(4)tBu)(2)(paco-Me(2)calix)] (26), in which the metallated calix[4]arene ligand is coordinated in a form reminiscent of the partial cone (paco) conformation of calix[4]arene. In these compounds, one of the methoxy groups is located inside the cavity of the calix[4]arene ligand. The complexes 24, 25 and 26 have been crystallographically characterised. Complexes with sterically more demanding phenolate ligands, namely 19 and 20 and the analogous zirconium complexes [Zr(O-4-C(6)H(4)Me)(2)(Me(2)calix)] (21) and [Zr(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (22) do not rearrange. Density functional calculations for the model complexes [M(OC(6)H(5))(2)(Me(2)calix)] with the calixarene possessing either cone or partial cone conformations are briefly presented.     

Eta6-mesityl,eta1-imidazolinylidene-carbene-ruthenium(II) complexes: catalytic activity of their allenylidene derivatives in alkene metathesis and cycloisomerisation reactions

The reaction of electron-rich carbene-precursor olefins containing two imidazolinylidene moieties [(2,4,6-Me(3)C(6)H(2)CH(2))NCH(2)CH(2)N(R)Cdbond;](2) (2a: R=CH(2)CH(2)OMe, 2 b R=CH(2)Mes), bearing at least one 2,4,6-trimethylbenzyl (R=CH(2)Mes) group on the nitrogen atom, with [RuCl(2)(arene)](2) (arene=p-cymene, hexamethylbenzene) selectively leads to two types of complexes. The cleavage of the chloride bridges occurs first to yield the expected (carbene) (arene)ruthenium(II) complex 3. Then a further arene displacement reaction takes place to give the chelated eta(6)-mesityl,eta(1)-carbene-ruthenium complexes 4 and 5. An analogous eta(6)-arene,eta(1)-carbene complex with a benzimidazole frame 6 was isolated from an in situ reaction between [RuCl(2)(p-cymene)](2), the corresponding benzimidazolium salt and cesium carbonate. On heating, the RuCl(2)(imidazolinylidene) (p-cymene) complex 8, with p-methoxybenzyl pendent groups attached to the N atoms, leads to intramolecular p-cymene displacement and to the chelated eta(6)-arene,eta(1)-carbene complex 9. On reaction with AgOTf and the propargylic alcohol HCtbond;CCPh(2)OH, compounds 4-6 were transformed into the corresponding ruthenium allenylidene intermediates (4-->10, 5-->11, 6-->12). The in situ generated intermediates 10-12 were found to be active and selective catalysts for ring-closing metathesis (RCM) or cycloisomerisation reactions depending on the nature of the 1,6-dienes. Two complexes [RuCl(2)[eta(1)-CN(CH(2)C(6)H(2)Me(3)-2,4,6)CH(2)CH(2)N- (CH(2)CH(2)OMe)](C(6)Me(6))] 3 with a monodentate carbene ligand and [RuCl(2)[eta(1)-CN[CH(2)(eta(6)-C(6)H(2)Me(3)-2,4,6)]CH(2)CH(2)N-(CH(2)C(6)H(2)Me(3)-2,4,6)]] 5 with a chelating carbene-arene ligand were characterised by X-ray crystallography.     

Unexpectedly efficient activation of push-pull nitriles by a Pt(II) center toward dipolar cycloaddition of Z-nitrones

Pt(II)-coordinated NCNR'(2) species are so highly activated towards 1,3-dipolar cycloaddition (DCA) that they react smoothly with the acyclic nitrones ArCH=N(+)(O(-))R' (Ar/R' = C(6)H(4)Me-p/Me; C(6)H(4)OMe-p/CH(2)Ph) in the Z-form. Competitive reactivity study of DCA between trans-[PtCl(2)(NCR)(2)] (R = Ph and NR'(2)) species and the acyclic nitrone 4-MeC(6)H(4)CH=N(+)(O(-))Me demonstrates comparable reactivity of the coordinated NCPh and NCNR'(2), while alkylnitrile ligands do not react with the dipole. The reaction between trans-[PtCl(2)(NCNR'(2))(2)] (R'(2) = Me(2), Et(2), C(5)H(10)) and the nitrones proceed as consecutive two-step intermolecular cycloaddition to give mono-(1a-d) and bis-2,3-dihydro-1,2,4-oxadiazole (2a-d) complexes (Ar/R' = p-tol/Me: R'(2) = Me(2)a, R'(2) = Et(2)b, R'(2) = C(5)H(10)c; Ar/R' = p-MeOC(6)H(4)/CH(2)Ph: R'(2) = Me(2)d). All complexes were characterized by elemental analyses (C, H, N), high resolution ESI-MS, IR, (1)H and (13)C{(1)H} NMR spectroscopy. The structures of trans-1b, trans-2a, trans-2c, and trans-2d were determined by single-crystal X-ray diffraction. Metal-free 5-NR'(2)-2,3-dihydro-1,2,4-oxadiazoles 3a-3d were liberated from the corresponding (dihydrooxadiazole)(2)Pt(II) complexes by treatment with excess NaCN and the heterocycles were characterized by high resolution ESI(+)-MS, (1)H and (13)C{(1)H} spectroscopy.     

Synthesis, structures, and reactivity of yttrium alkyl and alkynyl complexes with mixed Tp(Me2)/Cp ligands

The structurally characterized Tp(Me2)-supported rare earth metal monoalkyl complex (Tp(Me2))CpYCH(2)Ph(THF) (1) was synthesized via the salt-metathesis reaction of (Tp(Me2))CpYCl(THF) with KCH(2)Ph in THF at room temperature. Treatment of 1 with 1 equiv of PhC≡CH under the same conditions afforded the corresponding alkynyl complex (Tp(Me2))CpYC≡CPh(THF) (2). Complex 1 exhibits high activity toward carbodiimides, isocyanate, isothiocyanate, and CS(2); treatment of 1 with such substrates led to the formation of a series of the corresponding Y-C(benzyl) σ-bond insertion products (Tp(Me2))CpY[(RN)(2)CCH(2)Ph] (R = (i)Pr(3a), Cy(3b), 2,6-(i)Pr-C(6)H(3)(3c)), (Tp(Me2))CpY[SC(CH(2)Ph)NPh] (4), (Tp(Me2))CpY[OC(CH(2)Ph)NPh] (5), and (Tp(Me2))CpY(S(2)CCH(2)Ph) (6) in 40-70% isolated yields. Carbodiimides and isothiocyanate can also insert into the Y-C(alkynyl) σ bond of 2 to yield complexes (Tp(Me2))CpY[(RN)(2)CC≡CPh] (R = (i)Pr(7a), Cy(7b)) and (Tp(Me2))CpY[SC(C≡CPh)NPh] (9). Further investigation results indicated that 1 can effectively catalyze the cross-coupling reactions of phenylacetylene with carbodiimides. However, treatment of o-allylaniline with a catalytic amount of 1 gave only the benzyl abstraction product (Tp(Me2))CpY(NHC(6)H(4)CH(2)CH═CH(2)-o)(THF) (10), without observation of the expected organic hydroamination/cyclization product. All of these new complexes were characterized by elemental analysis and spectroscopic properties, and their solid-state structures were also confirmed by single-crystal X-ray diffraction analysis.     

Studies on the properties of organoselenium(IV) fluorides and azides

The reaction of organoselenides and -diselenides (R2Se and (RSe)2) with XeF2 furnished the corresponding organoselenium(IV) difluorides R2SeF2 (R=Me (1), Et (2), iPr (3), Ph (4), Mes (=2,4,6-(Me)3C6H2) (5), Tipp (=2,4,6-(iPr)3C6H2) (6), 2-Me 2NCH2C6H4 (7)), and trifluorides RSeF3 (R=Me (8), iPr (9), Ph (10), Mes (11), Tipp (12), Mes* (=2,4,6-(tBu) 3C6H2) (13), 2-Me2NCH2C6H4 (14)), respectively. In addition to characterization by multinuclear NMR spectroscopy, the first molecular structure of an organoselenium(IV) difluoride as well as the molecular structures of subsequent decomposition products have been determined. The substitution of fluorine atoms with Me3SiN3 leads to the corresponding organoselenium(IV) diazides R2Se(N3)2 (R=Me (15), Et (16), iPr (17), Ph (18), Mes (19), 2-Me 2NCH2C6H4 (20)) and triazides RSe(N3)3 (R=Me (21), iPr (22), Ph (23), Mes (24), Tipp (25), Mes* (26), 2-Me2NCH2C6H4 (27)), respectively. The organoselenium azides are extremely temperature-sensitive materials and can only be handled at low temperatures.     

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.     

PtII-mediated 1,3-dipolar cycloaddition of oxazoline N-oxides to nitriles as a key step to dihydrooxazolo-1,2,4-oxadiazoles

A novel type of heterocycle, viz., 2,3a-disubstituted 5,6-dihydro-3aH-[1,3]oxazolo[3,2-b][1,2,4]oxadiazoles, was generated by an intermolecular PtII-mediated 1,3-dipolar cycloaddition (1,3-DCA) between the oxazoline N-oxide C(Me)2CH2OC(R)=N+(O-) (R = Me, Et) and coordinated nitriles in the complexes trans/cis-[PtCl2(R'CN)2] [R' = Me, Et, CH2Ph, Ph, N(C5H10)]. The reaction is unknown for free RCN and oxazoline N-oxides, but under PtII-mediated conditions, it proceeds smoothly (CH2Cl2, 20-25 degrees C, 18-20 h) and gives pure complexes [PtCl2{N=C(R')ONC(R)OCH2CMe2}2] [R/R' = Me/Me, 1; Me/Et, 2; Me/CH2Ph, 3; Me/Ph, 4; Me/N(C5H10), 5; Et/Me, 6; Et/Et, 7; Et/CH2Ph, 8; Et/Ph, 9; Et/N(C5H10), 10] in 42-84% yields after column chromatography. Compounds 1-10 were characterized by elemental analyses (C, H, N), FAB+-MS, IR, and 1H and 13C{1H} NMR spectroscopies, and X-ray diffraction (for 1, 2, 5, and 9). With the exception of benzonitrile complexes, 1,3-DCA of oxazoline N-oxides to the PtII-ligated nitriles occurred diastereoselectively and afforded mixtures of enantiomers. Depending on the substituents on nitriles, asymmetric atoms in both of the formed heterocyclic ligands have the same (SS/RR) or different (SR/RS) configurations. The heterocyclic ligands were liberated from 1-4 and 6-9 by treatment with excess ethane-1,2-diamine (en) in CH2Cl2 for 1 day at 20-25 degrees C (for R' = Me, Et, CH2Ph) and at 50 degrees C (for R' = Ph) to achieve the free organic species and the well-known [Pt(en)2](Cl)2; the products were separated, and 2,3a-disubstituted 5,6-dihydro-3aH-[1,3]oxazolo[3,2-b][1,2,4]oxadiazoles (11-18) were characterized by ESI+-MS and 1H and 13C{1H} NMR spectroscopies.