Mononuclear and dinuclear palladium and nickel complexes of phosphinimine-based tridentate ligands

The tridentate bis-phosphinimine ligands O(1,2-C(6)H(4)N=PPh(3))(2)1, HN(1,2-C(2)H(4)N=PR(3))(2) (R = Ph 2, iPr 3), MeN(1,2-C(2)H(4)N=PPh(3))(2)4 and HN(1,2-C(6)H(4)N=PPh(3))(2)5 were prepared. Employing these ligands, monometallic Pd and Ni complexes O(1,2-C(6)H(4)N=PPh(3))(2)PdCl(2)6, RN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][Cl] (R = H 7, Me 8), [HN(1,2-CH(2)CH(2)N=PiPr(3))(2)PdCl][Cl] 9, [MeN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][PF(6)] 10, [HN(1,2-CH(2)CH(2)N=PPh(3))(2)NiCl(2)] 11, [HN(1,2-CH(2)CH(2)N=PR(3))(2)NiCl][X] (X = Cl, R = iPr 12, X = PF(6), R = Ph 13, iPr 14), and [HN(1,2-C(6)H(4)N=PPh(3))(2)Ni(MeCN)(2)][BF(4)]Cl 15 were prepared and characterized. While the ether-bis-phosphinimine ligand 1 acts in a bidentate fashion to Pd, the amine-bis-phosphinimine ligands 2-5 act in a tridentate fashion, yielding monometallic complexes of varying geometries. In contrast, initial reaction of the amine-bis-phosphinimine ligands with base followed by treatment with NiCl(2)(DME), afforded the amide-bridged bimetallic complexes N(1,2-CH(2)CH(2)N=PR(3))(2)Ni(2)Cl(3) (R = Ph 16, iPr 17) and N(1,2-C(6)H(4)N=PPh(3))(2)Ni(2)Cl(3)18. The precise nature of a number of these complexes were crystallographically characterized.     

Group 6 imido complexes supported by diamido-donor ligands

Reactions of the lithiated diamido-pyridine or diamido-amine ligands Li(2)N(2)N(py) or Li(2)N(2)N(am) with [W(NAr)Cl(4)(THF)] (Ar = Ph or 2,6-C(6)H(3)Me(2); THF = tetrahydrofuran) afforded the corresponding imido-dichloride complexes [W(NAr)(N(2)N(py))Cl(2)] (R = Ph, 1, or 2,6-C(6)H(3)Me(2), 2) or [W(NAr)(N(2)N(am))Cl(2)] (R = Ph, 3, or 2,6-C(6)H(3)Me(2), 4), respectively, where N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NSiMe(3))(2) and N(2)N(am) = Me(3)SiN(CH(2)CH(2)NSiMe(3))(2). Subsequent reactions of 1 with MeMgBr or PhMgCl afforded the dimethyl or diphenyl complexes [W(NPh)(N(2)N(py))R(2)] (R = Me, 5, or Ph, 6), respectively, which have both been characterized by single crystal X-ray diffraction. Reactions of Li(2)N(2)N(py) or Li(2)N(2)N(am) with [Mo(NR)(2)Cl(2)(DME)] (R = (t)Bu or Ph; DME = 1,2-dimethoxyethane) afforded the corresponding bis(imido) complexes [Mo(NR)(2)(N(2)N(py))] (R = (t)Bu, 7, or Ph, 8) and [Mo(N(t)Bu)(2)(N(2)N(am))] (9).     

Reactions of Li- and Yb-coordinated N,N'-bis(trimethylsilyl)-beta-diketiminates: one- and two-electron reductions, deprotonation, and C-N bond cleavage

The synthesis and characterisation of novel Li and Yb complexes is reported, in which the monoanionic beta-diketiminato ligand has been (i) reduced (SET or 2 [times] SET), (ii) deprotonated, or (iii) C-N bond-cleaved. Reduction of the lithium beta-diketiminate Li(L(R,R'))[L(R,R')= N(SiMe(3))C(R)CHC(R')N(SiMe(3))] with Li metal gave the dilithium derivative [Li(tmen)(mu-L(R,R'))Li(OEt(2))](R = R'= Ph; or, R = Ph, R[prime or minute]= Bu(t)). When excess of Li was used the dimeric trilithium [small beta]-diketiminate [Li(3)(L(R,R[prime or minute]))(tmen)](2)(, R = R'= C(6)H(4)Bu(t)-4 = Ar) was obtained. Similar reduction of [Yb(L(R,R'))(2)Cl] gave [Yb[(mu-L(R,R'))Li(thf)](2)](, R = R[prime or minute]= Ph; or, R = R'= C(6)H(4)Ph-4 = Dph). Use of the Yb-naphthalene complex instead of Li in the reaction with [Yb(L(Ph,Ph))(2)] led to the polynuclear Yb clusters [Yb(3)(L(Ph,Ph))(3)(thf)], [Yb(3)(L(Ph,Ph))(2)(dme)(2)], or [Yb(5)(L(Ph,Ph))(L(1))(L(2))(L(3))(thf)(4)] [L(1)= N(SiMe(3))C(Ph)CHC(Ph)N(SiMe(2)CH(2)), L(2)= NC(Ph)CHC(Ph)H, L(3)= N(SiMe(2)CH(2))] depending on the reaction conditions and stoichiometry. The structures of the crystalline complexes 4, 6x21/2(hexane), 5(C(6)D(6)), and have been determined by X-ray crystallography (and have been published).     

Coordination chemistry of diphenylphosphinoferrocenylthioethers on cyclooctadiene and norbornadiene rhodium(i) platforms

Complexes [RhCl(diene)(P,SR)] with chiral ferrocenyl phosphine-thioethers ligands (diene = norbornadiene, NBD, 1(R), or 1,5-cyclooctadiene, COD, 3(R); P,SR = CpFe(1,2-η(5)-C(5)H(3)(PPh(2))(CH(2)SR); R = tBu, Ph, Bz, Et) and the corresponding [Rh(diene)(P,SR)][BF(4)] (diene = NBD, 2(R); COD, 4(R)) have been synthesized from [RhCl(diene)](2) and the appropriate P,SR ligand. The molecular structure of the cationic complexes 2(tBu), 4(Ph) and 4(Bz), determined by single-crystal X-ray diffraction, shows the expected slightly distorted square planar geometry. For the neutral chloride complexes, a combination of experimental IR and computational DFT investigations points to an equally four coordinate square planar geometry with the diene ligand, the chlorine and the phosphorus atoms in the coordination sphere and with a dangling thioether function. However, a second isomeric form featuring a 5-coordinated square planar geometry with the thioether function placed in the axial position is easily accessible in some cases.     

Studies of a series of [Ni(P(R)2N(Ph)2)2(CH3CN)]2+ complexes as electrocatalysts for H2 production: substituent variation at the phosphorus atom of the P2N2 ligand

A series of [Ni(P(R)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) complexes containing the cyclic diphosphine ligands [P(R)(2)N(Ph)(2) = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), n-butyl (n-Bu), 2-phenylethyl (PE), 2,4,4-trimethylpentyl (TP), and cyclohexyl (Cy)] have been synthesized and characterized. X-ray diffraction studies reveal that the cations of [Ni(P(Bn)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) and [Ni(P(n-Bu)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(P(Bn)(2)N(Ph)(2))(2)] was also synthesized and characterized by X-ray diffraction studies and shown to have a distorted tetrahedral structure. These complexes, with the exception of [Ni(P(Cy)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2), all exhibit reversible electron transfer processes for both the Ni(II/I) and Ni(I/0) couples and are electrocatalysts for the production of H(2) in acidic acetonitrile solutions. The heterolytic cleavage of H(2) by [Ni(P(R)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) complexes in the presence of p-anisidine or p-bromoaniline was used to determine the hydride donor abilities of the corresponding [HNi(P(R)(2)N(Ph)(2))(2)](BF(4)) complexes. However, for the catalysts with the most bulky R groups, the turnover frequencies do not parallel the driving force for elimination of H(2), suggesting that steric interactions between the alkyl substituents on phosphorus and the nitrogen atom of the pendant amines play an important role in determining the overall catalytic rate.     

Chiral fluorous dialkoxy-diamino zirconium complexes: synthesis and use in stereospecific polymerization of 1-hexene

New catalysts for the isospecific polymerization of 1-hexene based on cationic zirconium complexes incorporating the tetradentate fluorous dialkoxy-diamino ligands [OC(CF(3))(2)CH(2)N(Me)(CH(2))(2)N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(2)NO)(2-)] and [OC(CF(3))(2)CH(2)N(Me)(1R,2R-C(6)H(10))N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(Cy)NO)(2-)] have been developed. The chiral fluorous diamino-diol [(ON(Cy)NO)H(2), 2] was prepared by ring-opening of the fluorinated oxirane (CF(3))(2)COCH(2) with (R,R)-N,N'-dimethyl-1,2-cyclohexanediamine. Proligand 2 reacts cleanly with [Zr(CH(2)Ph)(4)] and [Ti(OiPr)(4)] precursors to give the corresponding dialkoxy complexes [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3) and [Ti(OiPr)(2)(ON(Cy)NO)] (4), respectively. An X-ray diffraction study revealed that 3 crystallizes as a 1:1 mixture of two diastereomers (Lambda-3 and Delta-3), both of which adopt a distorted octahedral structure with trans-O, cis-N, and cis-CH(2)Ph ligands. The two diastereomers Lambda-3 and Delta-3 adopt a C(2)-symmetric structure in toluene solution, as established by NMR spectroscopy. Cationic complexes [Zr(CH(2)Ph)(ON(2)NO)(THF)(n)](+) (n=0, anion=[B(C(6)F(5))(4)](-), 5; n=1, anion=[PhCH(2)B(C(6)F(5))(3)](-), 6) and [Zr(CH(2)Ph)(ON(Cy)NO)(THF)](+)[PhCH(2)B(C(6)F(5))(3)](-) (7) were generated from the neutral parent precursors [Zr(CH(2)Ph)(2)(ON(2)NO)] (H) and [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3), and their possible structures were determined on the basis of (1)H, (19)F, and (13)C NMR spectroscopy and DFT methods. The neutral zirconium complexes H and 3 (Lambda-3/Delta-3 mixture), when activated with B(C(6)F(5))(3) or [Ph(3)C](+)[B(C(6)F(5))(4)](-), catalyze the polymerization of 1-hexene with overall activities of up to 4500 kg PH mol Zr(-1) h(-1), to yield isotactic-enriched (up to 74 % mmmm) polymers with low-to-moderate molecular weights (M(w)=4800-47 200) and monodisperse molecular-weight distributions (M(w)/M(n)=1.17-1.79).     

Oligomerization and regioselective hydrosilylation of styrenes catalyzed by cationic allyl nickel complexes bearing allylphosphine ligands

The complexes [Ni(eta(3)-CH(2)CHCH(2))Br(kappa(1)P-PR(2)CH(2)CH=CH(2))] (R = Ph 1, (i)Pr2 ) and [Ni(eta(3)-CH(2)C(R')CH(2))(kappa(1)P-PR(2)CH(2)CH=CH(2))(2)][BAr'(4)] (R' = H, R = Ph 4a, R = (i)Pr 4b; R' = CH(3), R = Ph 5a, R = (i)Pr 5b; Ar' = 3,5-C(6)H(3)(CF(3))(2)) have been prepared and characterized. The X-ray crystal structures of 1, 2 and 5b have been determined. 4a-b and 5a-b are catalyst precursors for the oligomerization of RC(6)H(4)CH=CH(2) to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH(3)) respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range from moderate to high. The oligomerization reactions are carried out in the temperature interval 25-40 degrees C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with a high isotactic fraction content P(m), with M(n) in the range 700-1900 Dalton, and polydispersities between 1.22 and 1.64. The cationic complexes 4a-b and 5a-b are also effective catalyst precursors for the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH(3) in 1,2-dichloroethane at 40 degrees C using an olefin/catalyst ratio equal to 100, leading selectively to RC(6)H(4)CH(SiH(2)Ph)CH(3) (R = H, CH(3)) in 50-79% yield.     

Syntheses of novel exo and endo isomers of ansa-substituted fluorophosphazenes and their facile transformations into spiro isomers in the presence of fluoride ions

Reactions of the dilithiated diols RCH2P(S)(CH2OLi)2 [R = Fc (1), Ph (2) (Fc = ferrocenyl)] with N3P3F6 in equimolar ratios at -80 degrees C result exclusively in the formation of two structural isomers of ansa-substituted compounds, endo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3a), Ph (4a)] and exo-RCH2P(S)(CH2O)2[P(F)N]2(F2PN) [R = Fc (3b), Ph (4b)], which are separated by column chromatography. Increasing the reaction temperature to -40 degrees C results in more of the exo isomers 3b and 4b at the expense of the endo isomers. The formation of the ansa-substituted compounds is found to depend on the dilithiation of the diols, as a reaction of the silylated phosphine sulfide FcCH2P(S)(CH2OSiMe3)2 (5) with N3P3F6 in the presence of CsF does not yield either 3a or 3b but instead gives the spiro isomer [FcCH2P(S)(CH2O)2 PN](F2PN)2 (6) as the disubstitution product of N3P3F6. The ansa isomers 3a and 3b are transformed into the spiro compound 6 in the presence of catalytic amounts of CsF at room temperature in THF, while 4a and 4b are transformed into the spiro compound [PhCH2P(S)(CH2O)2PN](F2PN)2 (7) under similar conditions. The novel conversions of ansa-substituted phosphazenes into spirocyclic phosphazenes were monitored by time-dependent 31P NMR spectroscopy. The effect of temperature on a transformation was studied by carrying out reactions at various temperatures in the range from -60 to +33 degrees C for 3b. In addition, compounds 3a, 3b, 4a, and 6 were structurally characterized. In the case of the ansa compounds, the nitrogen atom flanked by the bridging phosphorus sites was found to deviate significantly from the plane defined by the five remaining atoms of the phosphazene ring.     

Structural diversity in a family of copper(I) thioether complexes

Copper(I) complexes of the tridentate thioether ligands [PhB(CH(2)SCH(3))(3)] (abbreviated PhTt), [PhB(CH(2)SPh)(3)] (PhTt(Ph)), [PhB(CH(2)S(t)()Bu)(3)] (PhTt(t)()(Bu)), and [PhB(CH(2)S(p)()Tol)(3)] (PhTt(p)()(Tol)) and bidentate thioether ligands [Ph(2)B(CH(2)SCH(3))(2)] (Ph(2)Bt), [Et(2)B(CH(2)SCH(3))(2)] (Et(2)Bt), and [Ph(2)B(CH(2)SPh)(2)] (Ph(2)Bt(Ph)) have been prepared and characterized. The solution and solid state structures are highly sensitive to the identity of the borato ligand employed. Ligands possessing the smaller (methylthio)methyl donors, [PhTt] and [Ph(2)Bt], yielded tetrameric species, [(PhTt)Cu](4) and [(Ph(2)Bt)Cu](4), containing both terminal and bridging thioether ligation. The ligands containing the larger (arylthio)methyl groups, [PhTt(Ph)] and [PhTt(p)()(Tol)], form monomeric [PhTt(Ar)]Cu(NCCH(3)) in solution and one-dimensional extended structures in the solid state. Each complex type reacted cleanly with acetonitrile, pyridine, or triphenylphosphine generating the corresponding four-coordinate monomer, of which [PhTt(Ph)]Cu(PPh(3)), [PhTt(p)()(Tol)]Cu(PPh(3)), and [Et(2)Bt]Cu(PPh(3))(2) have been structurally characterized.     

Synthesis and structural characterization of an azatitanacyclobutene: the key intermediate in the catalytic anti-Markovnikov addition of primary amines to [small alpha]-alkynes

Reaction of the imidotitanium complexes [Ti(N(t)Bu)(N(2)N(py))(py)](1) and [Ti(N-2,6-C(6)H(3)(i)Pr(2))(N(2)N(py))(py)](2) with phenyl acetylene and tolyl acetylene in toluene gave the corresponding [2+2] cycloaddition products [Ti(N(2)N(py))[kappa(2)-N((t)Bu)CH[double bond]CR]](R = Ph:3, Tol:4) and [Ti(N(2)N(py))[kappa(2)-N(2,6-C(6)H(3)(i)Pr(2))CH[double bond]CR]](R = Ph:5, Tol: 6). Complex 6 is the first example of a key intermediate in the anti-Markovnikov addition of a primary amine to a terminal acetylene which has been structurally characterized by X-ray diffraction.     

Insertion of benzyl isocyanide into a Zr-P bond and rearrangement. Atom-economical synthesis of a phosphaalkene

Reaction of (N(3)N)ZrPHPh (N(3)N=N(CH(2)CH(2)NSiMe(3))(3)(3-)) with PhCH(2)N[triple bond]C affords the 1,1-insertion product (N(3)N)Zr[C(PHPh)=NCH(2)Ph], which thermally rearranges to the phosphaalkene-containing complex, (N(3)N)Zr[N(CH(2)Ph)C(H)=PPh].     

Preparation of the first examples of ansa-spiro substituted fluorophosphazenes and their structural studies: analysis of C-H...F-P weak interactions in substituted fluorophosphazenes

The reactions of fluorophosphazenes, endo ansa FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) (1) (Fc = ferrocenyl) and spiro [RCH(2)P(S)(CH(2)O)(2)PN](F(2)PN)(2) (R = Fc (2), C(6)H(5) (3)], with dilithiated diols have been explored. The study resulted in the formation of the first examples of ansa-spiro substituted fluorinated cyclophosphazenes as well as a bisansa substituted fluorophosphazene. The bisansa compound [1,3-[FcCH(2)P(S)(CH(2)O)(2)]][1,5-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (4) was found to be nongeminaly substituted with both the ansa rings in cis configuration, which is in stark contrast to the observations on cyclic chlorophosphazenes where geminal bisansa formation has been observed. The ansa-spiro compounds (5-7) underwent the ansa to spiro transformation leading to dispiro compounds in the presence of catalytic amounts of CsF at room temperature. Two of the ansa-spiro compounds, endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (5) and endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[FcCH(2)P(S)(CH(2)O)(2)]]N(3)P(3)F(2) (6), were structurally characterized, and the crystal structures indicate boat-chair conformation as well as crown conformation for the eight-membered ansa rings. Weak C-H.F-P interactions observed in the crystal structures of the ansa-spiro substituted fluorophosphazene derivatives have been analyzed and compared with C-H.F-P interactions of other fluorinated phosphazenes and thionyl phosphazenes.     

Chiral calcium catalysts for asymmetric hydroamination/cyclisation

Calcium complexes supported by chiral 1,2-diamines have been shown to be efficient catalysts for the asymmetric hydroamination of amino-olefin substrates; the calcium complexes [Ca(NN(R)){N(SiMe(3))(2)}(THF)] (R = (t)Bu, (i)Pr, Ph, 4-C(6)H(4)F) give enantioselectivities of up to 26% which marks a significant increase based upon literature precedence. The structure of [Ca(NN(Ph)){N(SiMe(3))(2)}(py)] has been computed with density functional methods.     

Rhodium(I) and Rhodium(III) complexes containing the chiral ligand 2,6-bis[4'(S)-isopropyloxazolin-2'-yl]pyridine (pybox): an unprecedented monohapto coordination of pybox

The complex [Rh(kappa(3)-N,N,N-pybox)(CO)][PF(6)] (1) has been prepared by reaction of the precursor [Rh(mu-Cl)(eta(2)-C(2)H(4))(2)](2), 2,6-bis[4'(S)-isopropyloxazolin-2'-yl]pyridine (pybox), CO, and NaPF(6). Complex 1 reacts with monodentate phosphines to give the complexes [Rh(kappa(1)-N-pybox)(CO)(PR(3))(2)][PF(6)] (R(3) = MePh(2) (2), Me(2)Ph (3), (C(3)H(5))Ph(2) (4)), which show a previously unseen monodentate coordination of pybox. Complex 1 undergoes oxidative addition reactions with iodine and CH(3)I leading to the complexes [RhI(R)(kappa(3)-N,N,N-pybox)(CO)][PF(6)] (R = I (5); R = CH(3) (6)). Furthermore, a new allenyl Rh(III)-pybox complex of formula [Rh(CH=C=CH(2))Cl(2)(kappa(3)-N,N,N-pybox)] (7) has been synthesized by a one-pot reaction from [Rh(mu-Cl)(eta(2)-C(2)H(4))(2)](2), pybox, and an equimolar amount of propargyl chloride.     

O(2) activation and hydrolysis of Salan rare-earth metal alkyl complexes

Salan ligated yttrium alkyl complex , L(1)Y(CH(2)SiMe(3))(THF) (Salan = L(1): [2-O-3,5-tBu(2)-C(6)H(2)CH(2)N(CH(3))CH(2)](2)), was exposed to an oxygen/nitrogen atmosphere to give a bimetallic alkoxide complex , [L(1)Y(mu-OCH(2)SiMe(3))](2). Whilst the lutetium counterparts (L(1)Lu(CH(2)SiMe(3))(THF)) and (L(2)Lu(CH(2)SiMe(3))(THF); L(2): [2-O-3-tBu-C(6)H(2)CH(2)N(CH(3))CH(2)](2)) were hydrolysed with moist nitrogen to afford mixed hydroxy/silyloxy complexes and ([L(1,2)Lu(mu-OSiMe(3))(mu-OH)LuL(1,2)]), respectively.     

Bis(phosphino)borates: a new family of monoanionic chelating phosphine ligands

The reaction of dimethyldiaryltin reagents Me(2)SnR(2) (R = Ph (1), p-MePh (2), m,m-Me(2)Ph (3), p-(t)BuPh (4), p-MeOPh (5), p-CF(3)Ph (6)) with BCl(3) provided a high-yielding, simple preparative route to the corresponding diarylchloroboranes R(2)BCl (R = Ph (10), p-MePh (11), m,m-Me(2)Ph (12), p-(t)BuPh (13), p-MeOPh (14), p-CF(3)Ph (15)). In some cases, the desired diarylchloroborane was not formed from an appropriate tin reagent Me(2)SnR(2) (R = o-MeOPh (7), o,o-(MeO)(2)Ph (8), o-CF(3)Ph (9)). The reaction of lithiated methyldiaryl- or methyldialkylphosphines with diarylchloroboranes or dialkylchloroboranes is discussed. Specifically, several new monoanionic bis(phosphino)borates are detailed: [Ph(2)B(CH(2)PPh(2))(2)] (25); [(p-MePh)(2)B(CH(2)PPh(2))(2)] (26); [(p-(t)BuPh)(2)B(CH(2)PPh(2))(2)] (27); [(p-MeOPh)(2)B(CH(2)PPh(2))(2)] (28); [(p-CF(3)Ph)(2)B(CH(2)PPh(2))(2)] (29); [Cy(2)B(CH(2)PPh(2))(2)] (30); [Ph(2)B(CH(2)P[p-(t)BuPh](2))(2)] (31); [(p-MeOPh)(2)B(CH(2)P[p-(t)BuPh](2))(2)] (32); [Ph(2)B(CH(2)P[p-CF(3)Ph](2))(2)] (33); [Ph(2)B(CH(2)P(BH(3))(Me)(2))(2)] (34); [Ph(2)B(CH(2)P(S)(Me)(2))(2)] (35); [Ph(2)B(CH(2)P(i)Pr(2))(2)] (36); [Ph(2)B(CH(2)P(t)Bu(2))(2)] (37); [(m,m-Me(2)Ph)(2)B(CH(2)P(t)Bu(2))(2)] (38). The chelation of diarylphosphine derivatives 25-33 and 36 to platinum was examined by generation of a series of platinum dimethyl complexes. The electronic effects of substituted bis(phosphino)borates on the carbonyl stretching frequency of neutral platinum alkyl carbonyl complexes were studied by infrared spectroscopy. Substituents remote from the metal center (i.e. on boron) have minimal effect on the electronic nature of the metal center, whereas substitution close to the metal center (on phosphorus) has a greater effect on the electronic nature of the metal center.     

Electrocatalytic oxidation of formate by [Ni(P(R)2N(R')2)2(CH3CN)]2+ complexes

[Ni(P(R)(2)N(R')(2))(2)(CH(3)CN)](2+) complexes with R = Ph, R' = 4-MeOPh or R = Cy, R' = Ph , and a mixed-ligand [Ni(P(R)(2)N(R')(2))(P(R'(2))N(R'(2)))(CH(3)CN)](2+) with R = Cy, R' = Ph, R' = Ph, have been synthesized and characterized by single-crystal X-ray crystallography. These and previously reported complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO(2), protons, and electrons, with rates that are first-order in catalyst and formate at formate concentrations below ～0.04 M (34 equiv). At concentrations above ～0.06 M formate (52 equiv), catalytic rates become nearly independent of formate concentration. For the catalysts studied, maximum observed turnover frequencies vary from <1.1 to 15.8 s(-1) at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. These catalysts are the only base-metal electrocatalysts as well as the only homogeneous electrocatalysts reported to date for the oxidation of formate. An acetate complex demonstrating an η(1)-OC(O)CH(3) binding mode to nickel has also been synthesized and characterized by single-crystal X-ray crystallography. Based on this structure and the electrochemical and spectroscopic data, a mechanistic scheme for electrocatalytic formate oxidation is proposed which involves formate binding followed by a rate-limiting proton and two-electron transfer step accompanied by CO(2) liberation. The pendant amines have been demonstrated to be essential for electrocatalysis, as no activity toward formate oxidation was observed for the similar [Ni(depe)(2)](2+) (depe = 1,2-bis(diethylphosphino)ethane) complex.     

Synthesis and characterisation of aluminium(III) and tin(II) complexes bearing quinoline-based N,N,O-tridentate ligands and their catalysis in the ring-opening polymerisation of ε-caprolactone

The synthesis and catalysis in the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) of aluminium(iii) and tin(ii) complexes supported by quinoline-based N,N,O-tridentate ligands are reported. Reaction of 8-{RC(O)CH(2)P(Ph(2)) = N}C(9)H(6)N (R = Bu(t), 2; R = Ph, 3) with AlMe(3) gave [Al(Me(2)){OCR = CHP(Ph(2)) = N(8-C(9)H(6)N)}] (R = Bu(t), 4; R = Ph, 5). Treatment of 2 and 3 with Sn[N(SiMe(3))(2)](2) generated tin(ii) complexes [Sn{OC(R) = CHP(Ph(2)) = N(8-C(9)H(6)N)}{N(SiMe(3))(2)}] (R = Bu(t), 6; R = Ph, 7). A similar reaction of AlMe(3) with 8-{MeC(O)CH(2)C(Me) = N}C(9)H(6)N gave [Al(Me(2)){OC(Me) = CHC(Me) = NC(9)H(6)N}] (9). Compounds 2-9 were characterised by NMR spectroscopy and elemental analysis. The molecular structures of complexes 4, 6 and 9 were determined by single crystal X-ray diffraction techniques. Investigation of catalysis of complexes 4-7 and 9 in the ROP of ε-CL revealed that the aluminium complexes, 4, 5 and 9, are much more active than the tin(ii) complexes. The kinetic studies for the polymerisation of ε-CL catalysed by complexes 4, 5 and 9 in the presence of benzyl alcohol (BnOH) indicated that the polymerisations proceed with the first-order dependence on monomer concentration. The polymerisation was well controlled and gave a polymer with narrow molecular weight distribution.     

Cyclopentadienylrhodium coordination to alkenylarenes

Photochemical reaction of [Rh(eta-C(5)H(5))(C(2)H(4))(2)] (5) with alkenyl benzene derivatives PhC(R(1))=CHR(2) results in the formation of four types of cyclopentadienylrhodium complexes: the mononuclear ethylene eta(2)-alkenylbenzene complexes [Rh(eta-C(5)H(5))(eta-C(2)H(4))(eta(2)-PhC(R(1))=CHR(2))] 9 a (R(1)=H, R(2)=Ph), 9 b (R(1)=Ph, R(2)=H), 9 c (R(1)=CH(3), R(2)=H), the mononuclear eta(4)-alkenylbenzene complex [Rh(eta-C(5)H(5))[beta,alpha,1,2-eta-C(6)H(5)C(Ph)=CH(2)]] (10), the dinuclear mu-eta(4):eta(4)-alkenylbenzene complex [anti-[Rh(eta-C(5)H(5))](2)[mu-beta,alpha,1,2-eta:3,4,5,6-eta-C(6)H(5)C(Ph)C=CH(2)]] (11), and the dinuclear rhodaindenyl complexes [Rh(eta-C(5)H(5))[1-3,8,9-eta-[1-(eta-C(5)H(5))]-3-R(1)-1-rhodaindenyl]] 12 a (R(1)=Ph), 12 b (R(1)=CH(3)). Reaction of 5 with triisopropenylbenzene gives the dinuclear complex [[Rh(eta-C(5)H(5))](2)(mu-beta,alpha,1,2-eta:beta',alpha',4,3-eta-C(6)H(3)[C(CH(3))=CH(2)](3))] (13). In the complexes 9, only the olefinic side chain of the alkenylbenzene binds to the metal. In the complexes 10, 11, 12, and 13, an arene nucleus coordinates to rhodium as a 1,3-diene moiety (or part thereof). The rhodaindenyl complexes 12 result from C-H activation of the alkenylbenzene at the beta and ortho positions. The crystal and molecular structures of 9 a, 9 b, 10, 11, and 12 a, b were determined. The role of 9-11 and 13 as models for intermediates during alkenylbenzene-assisted self-assembly of tricobalt clusters is discussed.     

An electrochemical and DFT study on selected beta-diketiminato metal complexes

Selected homoleptic metal beta-diketiminates M(I)L and M(II)L2 [M(I) = Li or K, M(II) = Mg, Ca or Yb; L: L(Ph) = [N(SiMe3)C(Ph)]2CH, L(Bu(t)) = N(SiMe3)C(Ph)C(H)C(Bu(t))N(SiMe3), L* = [N(C6H3Pr(i)2-2,6)C(Me)]2CH] have been studied by cyclic voltammetry (CV). The primary reduction (E(p)red, the peak reduction potential measured vs. SCE in thf containing 0.2 M [NBu4][PF6] with a scan rate 100 mV s(-1) at a vitreous carbon electrode at ambient temperature) is essentially ligand-centred: E(p)red being ca. -2.2 V (LiL(Ph) and KL(Ph)) and -2.4 V [Mg(L(Ph))2, LiL(Bu(t)) and Ca(L(Ph))2], while LiL* is significantly more resistant to reduction (E(p)red = -3.1 V). These observations are consistent with the view that the two (L(Ph)) or single (L(Bu(t))) C-phenyl substituent(s), respectively, are available for -electron-delocalisation of the reduced species, whereas the N-aryl substituents of L* are unable to participate in such conjugation for steric reasons. The primary reduction process was reversible on the CV-time scale only for LiL(Bu(t)), Ca(L(Ph))2 and Yb(L(Ph))2. For the latter this occurs at a potential ca. 500 mV positive of Ca(L(Ph))2, consistent with the notion that the LUMO of Yb(L(Ph))2 has substantial metal character. The successive reversible steps, each separated by ca. 500 mV, indicate that there is strong electronic communication between the two ligands of Yb(L(Ph))2. The overall three-electron transfer sequence shows that the final reduction level corresponds to [Yb(II)(L(Ph))2-(L(Ph))3-]. DFT calculations on complexes Li(L(Ph))(OMe2)2 and Li2(L(Ph))(OMe2)3 showed that both HOMO and LUMO orbitals are only based on the ligand with a HOMO-LUMO gap of 4.21 eV. Similar calculations on a doubly reduced complex Yb[(mu-L(Ph))Li(OMe2)]2 demonstrated that there is a considerable Yb atomic orbital contribution to the HOMO and LUMO of the complex.