Mixed amido/imido/guanidinato complexes of niobium: potential precursors for MOCVD of niobium nitride thin films

Novel mixed amido/imido/guanidinato complexes of niobium are reported. The complexes were synthesized by insertion of two equivalents of di-isopropylcarbodiimide (i-Pr-cdi) or bis-cyclohexylcarbodiimide (Cy-cdi) respectively, into the niobium-amido bonds of [Nb(NR(2))(3)(N-t-Bu)] (, R = Me; , R = Et) starting out from [NbCl(3)(N-t-Bu)(py)(2)] and the respective LiNR(2) reagent (py = pyridine). Four representative examples of these mixed ligand amido/imido/guanidinato compounds were synthesized and were characterized by (1)H-NMR, (13)C-NMR, (15)N-NMR, CHN-analysis, mass spectrometry and infra-red spectroscopy. The molecular structures of [Nb(NR(2)){eta(2)-(i-Pr-N)(2)C(NR(2))}(2)(N-t-Bu)] (, R = Me; , R = Et) in the solid state were determined by single-crystal X-ray diffraction studies and are discussed together with the molecular structure of the starting compound [Nb(NMe(2))(3)(N-t-Bu)] (). The thermal properties of the new compounds depend on the substitution at the guanidinato ligand. Complexes of i-Pr-cdi are significantly more volatile than complexes of Cy-cdi as revealed by thermogravimetric analysis. Preliminary experiments using as a single-molecule source for metal-organic chemical vapour deposition (MOCVD) in the absence of ammonia indicate the formation of the stoichiometric, and surprisingly carbon-free, cubic niobium nitride phase.     

Aluminum hydride cations stabilized by weakly coordinating carbaalanates

The reactions of t-BuCCLi with a mixture of AlH(3).NMe(3) and ClAlH(2).NMe(3) in boiling toluene with the addition of [t-BuCH(2)(Bzl)NMe(2)]Cl, or a bulky beta-diketimine instead, and [n-Bu(4)N]Cl led to the carbaalanates [H(2)Al(NMe(3))(2)](2)[(AlH)(8)(CCH(2)t-Bu)(6)], 3, and [n-Bu(4)N](2)[(AlH)(8)(CCH(2)t-Bu)(6)], 4, respectively. The reaction of Me(3)N.Al(CCt-Bu)(3) 5 and AlH(3).NMe(3) in boiling toluene yielded [H(n-Bu)Al(NMe(3))(2)][(AlH)(7)(AlNMe(3))(CCH(2)t-Bu)(6)], 6, in trace amounts. The single-crystal X-ray structures of 3 and 6 are reported. The compounds 3, 4, and 6 consist of well-separated ion pairs introducing carbaalanates as weakly coordinating anions and stabilizing aluminum hydride cations.     

Carbophosphazene-supported ligand systems containing pyrazole/guanidine coordinating groups

Carbophosphazene-based coordination ligands [{NC(NMe(2))}(2){NP(3,5-Me(2)Pz)(2)}] (1), [{NC(NEt)(2)}{NC(3,5-Me(2)Pz)}{NP(3,5-Me(2)Pz)(2)}] (2), [NC(3,5-Me(2)Pz)](2)[NP(3,5-Me(2)Pz)(2)] (3), [{NCCl}(2){NP(NC(NMe(2))(2))(2)}] (4), and [{NC(p-OC(5)H(4)N)}(2){NP(NC(NMe(2))(2))(2)}] (5) were synthesized and structurally characterized. In these compounds, the six-membered C(2)N(3)P ring is perfectly planar. The reaction of 1 with CuCl(2) afforded [{NC(NMe(2))}(2){NHP(O)(3,5-Me(2)Pz)}·{Cu(3,5-Me(2)PzH)(2)(Cl)}][Cl] (6). The ligand binds to Cu(II) utilizing the geminal [P(O)(3,5-Me(2)Pz)] coordinating unit. Similarly, the reaction of 2 with PdCl(2) afforded, after a metal-assisted P-N hydrolysis, [{NC(NEt)(2)}{NC(3,5-Me(2)Pz)}{NP(O)(3,5-Me(2)Pz)}·{Pd(3,5-Me(2)PzH)(Cl)}] (7). In the latter, the [P(O)(3,5-Me(2)Pz)] unit does not coordinate; in this instance, the Pd(II) is bound by a ring nitrogen atom and a carbon-tethered pyrazolyl nitrogen atom. The reaction of 3 with PdCl(2) also results in P-N bond hydrolysis affording [{NC(3,5-Me(2)Pz)(2)}{NP(O)(3,5-Me(2)Pz)}{Pd(Cl)}] (8). In contrast to 7, however, in 8, the Pd(II) elicits a nongeminal η(3) coordination from the ligand involving two carbon-tethered pyrazolyl groups and a ring nitrogen atom. Metalated products could not be isolated in the reaction of 3 with K(2)PtCl(4). Instead, a P-O-P bridged carbodiphosphazane dimer, [{NC(3,5-Me(2)Pz)NHC(3,5-Me(2)Pz)}{NP(O)}](2) (9), was isolated as the major product. Finally, the reaction of 5 with PdCl(2) resulted in [{NC(OC(5)H(4)N)}(2){NP(NC(NMe(2))(2))(2)}·{PdCl(2)}] (10). In the latter, the exocyclic P-N bonds are quite robust and are involved in binding to the metal ion. Compounds 6-10 have been characterized by a variety of techniques including X-ray crystallography. In all of the compounds, the bond parameters of the inorganic heterocyclic rings are affected by metalation.     

Synthesis of a bimetallic platinum-tungsten complex with a bridging micro-diboranyl-oxycarbyne moiety

The novel bimetallic micro-diboranyl-oxycarbyne bridged platinum-tungsten complex [W{eta(1),micro-CO-B(NMe(2))-B(NMe(2))-(eta(5)-C(5)H(4))}(CO)(2){Pt(PPh(3))(2)}] (W-Pt) () has been synthesised by a two-step reaction, starting from the dilithiated half-sandwich compound Li[W(eta(5)-C(5)H(4)Li)(CO)(3)] () via the ansa-diboranyl-oxycarbyne tungsten complex [W{eta(1)-CO-B(NMe(2))B(NMe(2))(eta(5)-C(5)H(4))}(OC)(2)] () by use of stoichiometric amounts of B(2)(NMe(2))(2)Br(2) and [Pt(eta(2)-C(2)H(4))(PPh(3))(2)], respectively.     

Zirconium and hafnium (1-pyridinio)imido complexes: functionalized terminal hydrazinediido analogues

Reaction of the diamidozirconium complex [Zr(N2(TBS)Npy)(NMe2)2] (1) (N2(TBS)Npy = CH3C(C5H4N)(CH2NSiMe2tBu)2) or the diamidohafnium complex [Hf(N2(TBS)Npy)(NMe2)2] (2) with one molar equiv. of 1-aminopyridinium triflate in the presence of one equiv. of pyridine gave the corresponding (1-pyridinio)imido complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(OTf)(py)] (3) and [Hf(N2(TBS)Npy)(=N-NC5H5)(OTf)(py)] (4). These were converted to the acetylide complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(CCPh)(py)] (5) and [Hf(N2(TBS)Npy)(=N-NC5H5)(CCPh)(py)] (6) by reaction with lithium phenylacetylide and substitution of the triflato ligand. Upon reaction of 3 and 4 with one molar equivalent of R-NC (R = tBu, Cy, 2,6-xyl), N-N bond cleavage in the (1-pyridinio)imido unit took place and the respective carbodiimido complexes [M(N2(TBS)Npy](N=C=NR)(OTf)(py)] (7-12) were formed instantaneously. A similar type of reaction with CO gave the isocyanato complex [Zr(N2(TBS)Npy](NCO)(OTf)(py)] (13). Finally, the abstraction of the pyridine ligand in compounds 3 and 4 with B(C6F5)3 led to the formation of the triflato-bridged dinuclear complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(OTf)]2 (14) and [Hf(N2(TBS)Npy)(=N-NC5H5)(OTf)]2 (15).     

A well-defined silica-supported dinuclear tungsten(III) amido species: synthesis, characterization and reactivity

Grafting of [W(2)(NMe(2))(6)] onto dehydroxylated silica affords the well-defined surface species [([triple bond, length as m-dash]Si-O)W(2)(NMe(2))(5)], characterized by elemental analysis, and infrared, Raman and NMR spectroscopies, and the catalytic reactivity of this supported tungsten(III) d(3)-d(3) dimer and of its alkoxide derivatives towards alkynes has been probed.     

Alternative reaction pathways in domino reactions of hydrazinediidozirconium complexes with alkynes

Reaction of [Zr{(NAr)(2)N(py)}(NMe(2))(2)] (Ar=3,5-xylyl: 2?a, mesityl: 2?b) with one or two molar equivalents of 1,1-diphenylhydrazine gave the mixed amido/hydrazido(1-) complex [Zr{(NMes)(2)N(py)}(HNNPh(2))(NMe(2))] (3), the bis-hydrazido complex [Zr{(NMes)(2)N(py)}(HNNPh(2))(2)] (4), and, in the presence of excess 4-dimethylaminopyridine (DMAP), hexacoordinate hydrazinediidozirconium complexes [Zr{(NXyl)(2)N(py)}(=NN(Me)Ph)(dmap)(2)] (5) and [Zr{(NXyl)(2)N(py)}(=NNPh(2))(dmap)(2)] (6). The reaction of one equivalent of the zirconium-hydrazinediide [Zr{(NTBS)(2)N(py)}(NNPh(2))(py)] (1) with disubstituted alkynes at RT for 16?h led to the formation of seven-membered diazazirconacycles 7?a-7?e in high yields. Similar reactivity was observed by reacting bis-amido complex 2?b with one molar equivalent of the corresponding alkyne and diphenylhydrazine. The formation of the seven-membered zirconacycles implied a key coupling step that involved the alkyne and one of the aryl rings of the diphenylhydrazinediido ligand. In some cases, such as the reaction with 2-butyne, the corresponding metallacycle was only obtained in modest yields (45?% for the reaction with 2-butyne) and a second major product, vinylimido complex 9, was formed in almost equal amounts (42?%) by 1,2-amination (formal insertion of the alkyne). The formation of compounds 7?a and 9 followed in part the same sequence of reaction steps and a key intermediate, an azirinido complex, represented a "bifurcation point" in the reaction network. Reaction of 1.2?equivalents of several diarylhydrazines and various substituted alkynes (1?equiv) at ambient temperature (or at 80?°C) in the presence of 10?mol?% [Zr{(NXyl)(2)N(py)}(NMe(2))(2)] (2?a) gave the corresponding indole derivatives. On the other hand, the replacement of 1,1-diarylhydrazines by 1-methyl-1-phenyl hydrazine led to head-to-head cis-1,3-enynes in good yields.     

Tungsten imido complexes as precursors to tungsten carbonitride thin films

Thin films of tungsten carbonitride have been formed on glass by low-pressure chemical vapour deposition (LP)CVD at 550 degrees C from four closely related precursors: [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2), [W(N(t)Bu)(2)Cl(2)(TMEDA)] (TMEDA = N,N,N',N'-tetramethylethylenediamine), [W(N(t)Bu)(2)Cl(2)(py)(2)] (py = pyridine) and [W(N(t)Bu)(2)Cl(N{SiMe(3)}(2))]. The grey mirror-like films were grown with a nitrogen or ammonia bleed gas. In all cases the chlorine content of the deposited films was less than 1 at% and the oxygen content of the films was lower for those grown using ammonia. Surprisingly, the use of ammonia did not significantly change the carbon content of the resulting films. Despite the coordination environment around the metal being essentially the same and the materials having a comparable volatility, some differences in film quality were observed. The films were uniform, adhesive, abrasion resistant, conformal and hard, being resistant to scratching with a steel scalpel. X-Ray powder diffraction patterns of all the films showed the formation of beta-WN(x)C(y). As a comparison the aerosol-assisted chemical vapour deposition (AA)CVD of [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2) was investigated and amorphous tungsten carbonitride films were deposited.     

Double-stranded W/Ag/S chain structure generated from [syn-(WO(NCS)(2))(2)(mu-S)(2)] building blocks

The dimeric W(V) complex [Et(4)N](4)[syn-(O=W(NCS)(3))(2)(mu-S)(2)], 1, prepared from [Et(4)N](2)[WS(4)], SCN(-), and Cd(2+), shows interesting reactivity patterns in that the thiocyanate trans to the oxo group can in part be replaced, initiated by Mn(2+), by dimethylformamide (DMF) to form [Et(4)N](2.5)[(O=W(NCS)(2.25)(DMF)(1.25))(2)(mu-S)(2)], 2. With Ag(+), 1 undergoes partial replacement of SCN(-) by DMF and coordinates to the silver ions to generate ([Et(4)N](2.5)[(W(2)O(2)(NCS)(2)(mu-S)(2))(mu-NCS)(2)(DMF)(Ag(0.5)(SCN))])(n), 3. Compound 3 constitutes a polymeric double-stranded chain, with normal bonding interactions [via W-(mu-NCS)-Ag] between the two strands, and moderate intrastrand [W-(mu-NCS).Ag] bonding. The crystal and molecular structures of the three compounds are described.     

Synthesis and structural investigation of tungsten imido amidinate and guanidinate complexes

The tungsten imido guanidinate and amidinate complexes W(NR)Cl(3)[R'NC(NMe(2))NR'] and W(NR)Cl(3)[R'NC(Me)NR'] (R = Ph, (i)Pr, Cy; R' = (i)Pr, (t)Bu, TMS) were synthesized by reacting the corresponding imido complex W(NR)Cl(4)(OEt(2)) with the appropriate lithium amidinate or guanidinate. Crystallographic structure determination of W(N(i)Pr)Cl(3)[(i)PrNC(NMe(2))N(i)Pr] and W(N(i)()Pr)Cl(3)[(i)PrNC(Me)N(i)Pr] allows comparison of structural features between the guanidinate and amidinate ligand in the presence of an identical ancillary ligand set.     

Tuning the redox potentials of dinuclear tungsten oxo complexes [(Cp*W(4,4'-R,R-2,2'-bpy)(mu-O))2][PF6]2 toward photochemical water splitting

A series of novel dinuclear tungsten(IV) oxo complexes with disubstituted 4,4'-R,R-2,2'-bipyridyl (R(2)bpy) ligands of the type [(Cp*W(R(2)bpy)(mu-O))(2)][PF(6)](2) (R=NMe(2), tBu, Me, H, Cl) was prepared by hydrolysis of the tungsten(IV) trichloro complexes [Cp*W(R(2)bpy)Cl(3)]. Cyclic voltammetry measurements for the tungsten(IV) oxo compounds provided evidence for one reversible oxidation and two reversible reductions leading to the oxidation states W(V)W(IV), W(IV)W(III) and W(III)W(III). The corresponding complexes [(Cp*W(R(2)bpy)(mu-O))(2)](n+) [PF(6)](n) (n=0 for R=Me, tBu, and 1, 3 for both R=Me) could be isolated after chemical oxidation/reduction of the tungsten(IV) oxo complexes. The crystal structures of the complexes [(Cp*W(R(2)bpy)(mu-O))(2)][BPh(4)](2) (R=NMe(2), tBu) and [(Cp*W(Me(2)bpy)(mu-O))(2)](n+)[PF(6)](n) (n=0, 1, 2, 3) show a cis geometry with a puckered W(2)O(2) four-membered ring for all compounds except [(Cp*W(Me(2)bpy)(mu-O))(2)] which displays a trans geometry with a planar W(2)O(2) ring. Examining the interaction of these novel tungsten oxo complexes with protons, we were able to show that the W(IV)W(IV) complexes [(Cp*W(R(2)bpy)(mu-O))(2)][PF(6) (-)](2) (R=NMe(2), tBu) undergo reversible protonation, while the W(III)W(III) complexes [(Cp*W(R(2)bpy)(mu-O))(2)] transfer two electrons forming the W(IV)W(IV) complex and molecular hydrogen.     

Synthesis and characterization of thermally robust amidinato group 13 hydride complexes

The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga.     

Synthesis and characterisation of new titanium amino-alkoxides: precursors for the formation of TiO2 materials

Reaction of the amino-alkoxides HOCH(CH(2)NMe(2))(2) (Hbdmap) and HOC(CH(2)NMe(2))(3) (Htdmap) with [Ti(OR)(4)] yields a series of heteroleptic titanium alkoxides [Ti(OR)(4-n)(L)(n)] (L = bdmap, tdmap). Substitution of the monodentate alkoxide with the chelating alkoxides becomes progressively more difficult, with homogeneous products being obtained only for n = 1, 2. The structure of [Ti(OEt)(3)(bdmap)](2), a mu-OEt bridged dimer, has been determined. Hydrolysis of [Ti(OR)(2)(L)(2)], by adventitious moisture affords the dimeric oxo-alkoxides [Ti(O)(L)(2)](2), both of which have been characterised crystallographically. These two compounds have also been prepared by reaction of [Ti(NMe(2))(2)(L)(2)] with the hydrated metal salts [Zn(acac)(2).2H(2)O] and [Zn(OAc)(2).2H(2)O] using the intrinsic water molecules in these salts to react with the labile amido groups, though the former also produces Me(Me(2)N)C=C(H)C(O)Me from reaction of liberated HNMe(2) with the coordinated acac ligand, while the latter also affords the ligand exchange product [Zn(OAc)(bdmap)]. In neither case does the free dimethylamino group of [Ti(O)(L)(2)](2) coordinate a second metal. The dimeric structure of [Zn(OAc)(bdmap)](2) has been established, and the structure of the tetrameric oxo-alkoxide [Ti(O)(OPr(i))(OCH(2)CH(2)NMe(2))](4) is reported for comparison with others in this study. [Ti(OEt)(3)(bdmap)](2) has been used as a precursor in AACVD (Aerosol-Assisted Chemical Vapour Deposition) to generate amorphous TiO(2) films on glass at 440 degrees C, and TiO(2)@C nanoparticles of approximate diameter 350 nm with a carbon coating of width ca. 75 nm on heating in a sealed container at 700 degrees C.     

General synthesis of (salen)ruthenium(III) complexes via N...N coupling of (salen)ruthenium(VI) nitrides

Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.     

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitride MOCVD

The coordination chemistry of the hydrazine derivatives dimethylhydrazine (Hdmh) and N-trimethylsilyl-N'N'-dimethylhydrazine (Htdmh) at Ta, Zr and Hf was investigated aiming at volatile mixed ligand all-nitrogen coordinated compounds. The hydrazido ligands were introduced either by salt metathesis employing the Li salts of the hydrazines and the tetrachlorides MCl(4) (M = Zr, Hf) or by amine substitution using M(NR(2))(4) (R = Me, Et) and [(t-BuN)Ta(NR(2))(3)]. The new complexes were fully characterised including (1)H/(13)C NMR, mass spectrometry and a study of their thermal behaviour. The crystal structures of [ZrCl(tdmh)(3)] and the all-nitrogen coordinated complex [Ta(N-t-Bu)(NMe(2))(2)(tdmh)] are discussed as well as the structure of the by-product [Li(tdmh)(py)](2). Preliminary MOCVD experiments of the liquid compound [Ta(NEt(2))(2)(N-t-Bu)(tdmh)] were performed and the deposited TaN(Si) films were analysed by RBS and SEM.     

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).     

The synthesis of W-O-W μ-oxo clusters by hydrolysis of tungsten aminoalkoxides and their structural characterisation

The tungsten aminoalkoxides W(O)(OPr(i))(3)L [L = dmae, OCH(2)CH(2)NMe(2) (1); bdmap, OCH(CH(2)NMe(2))(2) (2); tdmap, OC(CH(2)NMe(2))(3) (3)] have been synthesised. Controlled hydrolysis of 1-3 has allowed isolation of W(4)O(4)(μ-O)(6)(dmae)(4) (4), W(4)O(4)(μ-O)(4)(OPr(i))(4)(bdmap)(4) (5), W(6)O(6)(μ-O)(9)(tdmap)(6) (6), W(4)O(4)(μ-O)(6)(tdmap)(4) (7), W(4)O(4)(μ-O)(6)(tdmap)(4)·4H(2)O (7a), all of which have been characterised by X-ray crystallography. 4, 7, 7a each embody a W(4)O(6) core with adamantane structure, 5 incorporates a folded W(4)O(4) square and 6 has a trigonal prismatic W(6)O(9) at its heart. 7 decomposes in air at to give orthorhombic WO(3), while 1-3 decomposed under an autogenerated pressure (Reaction under Autogenic Pressure at Elevated Temperatures, RAPET) to form mixtures of carbon-coated WO(x) needles and carbon spherules.     

Formation of the imide [Ta(NMe2)3(μ-NSiMe3)]2 through an unprecedented α-SiMe3 abstraction by an amide ligand

Ta(NMe(2))(4)[N(SiMe(3))(2)] (1) undergoes the elimination of Me(3)Si-NMe(2) (2), converting the -N(SiMe(3))(2) ligand to the ═NSiMe(3) ligand, to give the imide "Ta(NMe(2))(3)(═NSiMe(3))" (3) observed as its dimer 4. CyN═C═NCy captures 3 to yield guanidinates Ta(NMe(2))(3-n)(═NSiMe(3))[CyNC(NMe(2))NCy](n) [n = 1 (5), 2 (6)]. The kinetic study of α-SiMe(3) abstraction in 1 gives ΔH(?) = 21.3(1.0) kcal/mol and ΔS(?) = -17(2) eu.     

The structural characteristics of organozinc complexes incorporating N,N'-bidentate ligands

Dimethylzinc reacts with an excess of N-2-pyridylaniline 6 to give the homoleptic species, Zn[PhN(2-C(5)H(4)N)](2) 8. Single crystal X-ray diffraction reveals a solid-state dimer based on an 8-membered (NCNZn)(2) core motif. Zn[CyN(2-C(5)H(4)N)]Me (Cy =c-C(6)H(11)) 10, prepared by the combination of ZnMe(2) with the corresponding cyclohexyl-substituted pyridylamine, is also dimeric in the solid state but reveals a central (ZnN)(2) metallacycle. Employment of (p-Tol)NH(2-C(5)H(4)N)(p-Tol = 4-MeC(6)H(4)) 11 yielded the tris(zinc) adduct Zn(3)[(p-Tol)N(2-C(5)H(4)N)](4)Me(2) 12, which incorporates a central chiral molecule of 'Zn[(p-Tol)N(2-C(5)H(4)N)](2)' 12a, that bridges two 'Zn[(p-Tol)N(2-C(5)H(4)N)]Me' 12b units. A similar trimetallic structure is noted when the pyridylaniline substrate 11 is replaced with the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), affording Zn(3)(hpp)(4)Me(2) 13. Spectroscopic studies point to retention of the solid-state structure of in hydrocarbon solution. Reaction of 13 with dimesityl borinic acid, Mes(2)BOH (Mes = mesityl), affords Zn(3)(hpp)(4)(OBMes(2))(2) 14 in which the trimetallic core is retained. This reactivity is in contrast to the closely related reaction of dimeric Zn[Me(2)NC[N(i)Pr](2)]Me 15 with Mes(2)BOH, which yielded Zn[Me(2)NC[N(i)Pr](2)][OBMes(2)].Me(2)NC[N(i)Pr][NH(i)Pr] 16 as a result of protonation at the guanidine ligand in addition to the Zn-Me bond.     

Synthesis of zinc trisubstituted hydrazido complexes and ortho-metalation of 4-(dimethylamino)pyridine

The zinc hydrazide complexes [EtZn(N(SiMe(3))NMe(2))](2), [EtZn(N(Me)NMe(2))](4), and Zn(3)Et(4)(N(Et)NMe(2))(2) were synthesized by allowing excess hydrazine, HN(R)NMe(2), to react with diethyl zinc. The product of the reaction between ZnEt(2) and HN(i-Pr)NMe(2)ortho-metalated 4-(dimethylamino)pyridine (DMAP) at room temperature, producing the complex Zn[(NC(5)H(3)-p-NMe(2))ZnEt(N(i-Pr)NMe(2))](2). At elevated temperatures, Zn(3)Et(4)(N(Et)NMe(2))(2) also ortho-metalated DMAP, but [EtZn(N(Me)NMe(2))](4) did not. Single-crystal X-ray diffraction studies revealed that the hydrazide ligands in [EtZn(N(SiMe(3))NMe(2))](2) act as bridging mono-hapto amide ligands, and in Zn(3)Et(4)(N(Et)NMe(2))(2) and Zn[(NC(5)H(3)-p-NMe(2))ZnEt(N(i-Pr)NMe(2))](2) the hydrazide ligands are di-hapto.