Syntheses of new ionic technetium(III) complexes containing four monodentate phosphine ligands. Crystal structures of trans-[Tc(PMe2Ph)4Cl2]PF6, trans-[Tc(PMe3)4Cl2]BPh4, and trans-[Tc(PMe3)4Cl2]PF6

New ionic technetium complexes of the type trans-[Tc(PR3)4Cl2]+ are synthesized by various methods. The simplest method is the reaction of [TcO4]- with the phosphine in methanol in the presence of a chloride salt. Compounds containing PMe2Ph and PMe3 are synthesized and characterized by crystallographic methods. The complexes containing the less bulky phosphine can be prepared from complexes containing the bulker phosphine. The compounds are paramagnetic, with two unpaired electrons. The complexes studied by X-ray diffraction methods are the trans isomers. [Tc(PMe2Ph)4Cl2]PF6 crystallizes in the monoclinic space group P2(1)/c, with a = 11.511(2) A, b = 26.713(7) A, c = 12.688(3) A, beta = 92.79(1) degrees, Z = 4, and R1 = 0.0574. [Tc(PMe3)4Cl2]BPh4 (II) crystallizes in the orthorhombic space group Pbcn, with a = 18.213(5) A, b = 22.950(5) A, c = 19.428(6) A, Z = 8, and R1 = 0.0691. [Tc(PMe3)4Cl2]PF6 crystallizes in the monoclinic space group P2(1)/c, with a = 18.152(7) A, b = 16.838(9) A, c = 18.090(6) A, beta = 106.63(1) degrees, Z = 8, and R1 = 0.0670. The compounds all have octahedral coordination, but an important tetrahedral deformation of the plane containing the Tc and the four P atoms is observed in each case. In II, the two independent Tc atoms are both located on 2-fold axes.     

Unusual Structure,Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3]

The reactions of bis(borohydride) complexes [(RN?)Mo(BH₄)₂(PMe₃)₂] ( 4 : R=2,6‐Me₂C₆H₃; 5 : R=2,6‐iPr₂C₆H₃) with hydrosilanes afford new silyl hydride derivatives [(RN?)Mo(H)(SiR′₃)(PMe₃)₃] ( 3 : R=Ar, R′₃=H₂Ph; 8 : R=Ar′, R′₃=H₂Ph; 9 : R=Ar, R′₃=(OEt)₃; 10 : R=Ar, R′₃=HMePh). These compounds can also be conveniently prepared by reacting [(RN?)Mo(H)(Cl)(PMe₃)₃] with one equivalent of LiBH₄ in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe₃ group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non‐Bailar‐twist pathway. The silyl/silane exchange proceeds through an unusual Mo^VI intermediate, [(ArN?)Mo(H)₂(SiH₂Ph)₂(PMe₃)₂] ( 19 ). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans‐(ArN)Mo(OiPr)(SiH₂Ph)(PMe₃)₂] ( 18 ). This latter species does not undergo the elimination of a Si? O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β‐CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN?)Mo(η²‐PhC(O)H)₂(PMe₃)], which reacts further with hydrosilane through a η¹‐silane complex, as studied by DFT calculations.     

The cis-effect in trans-[PtCl2XY] compounds

The cis-influence observed in chlorine NQR data of X, Y affecting the Pt-Cl bonds in compounds of type trans-[PtCl₂XY] is interpreted. -bonding differences in Pt-Cl bonds are suggested to account for the trends in NQR frequencies. Pt-Cl -bonding is negligibly small for both d (Pt)–p (Cl) and p –p (Cl) interactions.     

Preparation and properties of dinitrogen complexes of molybdenum and tungsten with trimethylphosphine as coligand : III. Synthesis and properties of cis-[W(N2)2(PMe3)4], trans-[W(C2H4)2(PMe3)4] and [M(N2)(PMe3)5] (M = Mo,W). The crystal and molecular structure of [Mo(N2)(PMe3)5]

The reduction of [WCl₄(PMe₃)₃] with dispersed sodium, under dinitrogen, gives cis-[W(N₂)₂(PMe₃)₄], while under ethylene trans-[W(C₂H₄)₂(PMe₃)₄] is obtained. The ethylene complex can also be prepared by displacement of the dinitrogen molecules in cis-[W(N₂)₂(PMe₃)₄] by ethylene at room temperature and pressure. Interaction of cis-[M(N₂)₂(PMe₃)₄] complexes (M = Mo, W), with PMe₃, under helium or argon, yields [M(N₂)(PMe₃)₅]. The molybdenum complex crystallizes in the orthorhombic space group Pnma, with a 22.063(6), b 12.106(4), c 9.745(4) Å. The Mo—P distance trans to the dinitrogen ligand (2.483(7) Å) is slightly longer than the average of the other four Mo—P bonds (2.460(5) Å).     

Synthese von Nitrenkomplexen mit N-Trimethylsilylanilin. II. Charakterisierung und Kristallstruktur der Rhenium(V)-phenylnitren-Komplexe mer-[Re(NPh)Cl3(NH2Ph)(Ph3P)] und trans-[Re(NPh)(OMe)Cl2(Ph3P)2]

Synthesis of Phenylnitrene Complexes with N-Trimethylsilylaniline. II. Characterization and Crystal Structure of the Rhenium(V) Complexes mer-[Re(NPh)Cl₃(NH₂Ph)(Ph₃P)] and trans-[Re(NPh)(OMe)Cl₂(Ph₃P)₂] Reaction of [ReOCl₃(Ph₃P)₂] with N-trimethylsilylaniline yields mer-[Re(NPh)Cl₃(Ph₃P)₂], which reacts under air with excess of N-trimethylsilylaniline to form [Re(NPh)Cl₃ · (NH₂Ph)(Ph₃P)]. Crystallization from CH₂Cl₂/MeOH affords [Re(NPh)(OMe)Cl₂(Ph₃P)₂] as an additional product. [Re(NPh)Cl₃(NH₂Ph)(Ph₃P)] crystallizes in the monoclinic space group P2₁/n with a = 1 192.3(3); b = 1 918.9(3); c = 1 266.3(3) pm; β = 101.71(1)°; Z = 4. The rhenium atom has a distorted octahedral environment with the Cl atoms in meridional positions. The phenyl nitrene ligand is coordinated with an almost linear arrangement Re? N1? C40 = 166.8(6)° and with a bond distance Re?N = 170.5(6) pm. [Re(NPh)(OMe)Cl₂(Ph₃P)₂] · 1/2CH₂Cl₂ crystallizes in the triclinic space group P1 : a = 1 103.1(4); b = 1 227.9(4); c = 1 711.3(5) pm; α = 70.48(3)°; β = 72.71(3)°; γ = 80.03(3)°; Z = 2. The rhenium atom exhibits a distorted octahedral coordination with the Cl atoms and the phosphine ligands in trans positions. As a consequence of the competition of the nitrene ligand and the trans-coordinated methoxy group the Re?;N bond length is slightly lengthened to 173.2(7) pm, while the Re? O bond length of 193.4(6) pm is short. The bond angles Re? N? C70 and Re? O? C80 are 173.3(7)° and 139.1(7)°, respectively.     

The preparation and molecular structure oftrans-[MoCl2(PMe2Ph)4]

Summary The compoundtrans-[MoCl₂(PMe₂Ph)₄] has been prepared by the reduction of MoCl₅ (by Mg) or of [MoCl₃(PMe₂Ph)₃] (by LiBuⁿ) in the presence of PMe₂Ph in tetrahydrofuran (THF). It has _eff=2.84 B.M. and crystallises in space group P1 witha=11.591(3),b=12.931(3),c=12.703(3) Å, = 95.28(2), =105.97(2), =103.54(2)°. Refinement of the structure gave R=0.036. The Mo-Cl and Mo-P distances average 2.443(6) and 2.534(8) Å, respectively.Low-valent phosphine complexes of the Group VI metals continue to attract much attention because of their involvement in studies of the catalytic activation of dinitrogen⁽¹⁾, dihydrogen(^{2, 3}), alkenes and alkynes(⁴). As a by-product during our studies of dinitrogen(¹) and hydride(²) complexes of molybdenum and tungsten, we obtainedtrans-[MoCl_2- (PMe₂Ph)₄] as yellow, paramagnetic crystals (_eff= 2.84 B.M.). We first obtained the compound during the attempted synthesis ofcis-[Mo(N₂)₂(PMe₂Ph)₄] by reduction of MoCl₅ with Mg in the presence of PMe₂Ph (see Experimental). Upon identification of the compound we found that it could be readily synthesised by treatment of [MoCl₃(PMe₂Ph)₃]⁽⁵⁾ with LiBuⁿ in THF in the presence of PMe₂Ph (experimental).The complex was shown to have thetrans structure by x-ray analysis (Figure). Analogues oftrans-[MoCl₂(PMe₂Ph)₄] have been prepared, namely [CrCl₂(Me₂PCH₂CH₂PMe₂)₂]⁽⁶⁾,trans- [MoCl₂(PMe₃)₄]⁽⁷⁾, [WCl₂(PMe₂Ph)₄]⁽⁸⁾ and [WCl₂(PMe₃)₄]⁽⁴⁾, of which onlytrans-[MoCl₂(PMe₃)₄] has been examined by X-rays⁽⁷⁾. Its principal structural parametersi.e. d(Mo-Cl)= 2.420(6), d(Mo-P)_av=2.496(3) Å⁽⁶⁾ are close to those found here fortrans-[MoCl₂(PMe₂Ph)₄].     

Kinetics and mechanism for reduction of the anticancer prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by thiols

The reduction of the platinum(IV) prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by L-cysteine, DL-penicillamine, DL-homocysteine, N-acetyl-L-cysteine, 2-mercaptopropanoic acid, 2-mercaptosuccinic acid, and glutathione has been investigated at 25 degrees C in a 1.0 M aqueous perchlorate medium with 6.8 < or = pH < or = 11.2 using stopped-flow spectrophotometry. The stoichiometry of Pt(IV):thiol is 1:2, and the redox reactions follow the second-order rate law -d[Pt(IV)]/dt = k[Pt(IV)][RSH]tot, where k denotes the pH-dependent second-order rate constant and [RSH]tot the total concentration of thiol. The pH dependence of k is ascribed to parallel reductions of JM335 by the various protolytic species of the thiols, the relative contributions of which change with pH. Electron transfer from thiol (RSH) or thiolate (RS-) to JM335 is suggested to take place as a reductive elimination process through an attack by sulfur at one of the mutually trans chloride ligands, yielding trans-[Pt(OH)2(c-C6H11NH2)(NH3)] and RSSR as the reaction products, as confirmed by 1H NMR. Second-order rate constants for the reduction of JM335 by the various protolytic species of the thiols span more than 3 orders of magnitude. Reduction with RS- is approximately 30-2000 times faster than with RSH. The linear correlation log(kRS) = (0.52 +/- 0.06)-pKRSH--(2.8 +/- 0.5) is observed, where kRS denotes the second-order rate constant for reduction of JM335 by a particular thiolate RS- and KRSH is the acid dissociation constant for the corresponding thiol RSH. The slope of the linear correlation indicates that the reactivity of the various thiolate species is governed by their proton basicity, and no significant steric effects are observed. The half-life for reduction of JM335 by 6 mM glutathione (40-fold excess) at physiologically relevant conditions of 37 degrees C and pH 7.30 is 23 s. This implies that JM335, in clinical use, is likely to undergo in vivo reduction by intracellular reducing agents such as glutathione prior to binding to DNA. Reduction results in the immediate formation of a highly reactive platinum(II) species, i.e., the bishydroxo complex in rapid protolytic equilibrium with its aqua form.     

Reactions oftrans-[Mo(CNMe)2(PMe2Ph)4] andmer-[W(CNMe)3(PMe2Ph)3] complexes with methanol and with mineral acids to give amines,ammonia and hydrocarbons

Summary Treatment oftrans-[Mo(CNMe)₂(PMe₂Ph)₄] andme-[W(CNMe)₃(PMe₂Ph)₃] with sulphuric or hydrochloric acids in methanol or ethanol, or in methanol alone, under irradiation, gives methylamine, ammonia and hydrocarbons (mainly methane). The complex [W₂(CNMe)₄(-CNHMe)₂(PMe₂Ph)₄]²⁺ cation has been obtained by the treatment ofmer-[W(CNMe)₃(PMe₂Ph₃] with H₂SO₄ or [Et₂OH][BF₄] and gives methylamine, ammonia and methane on further acid treatment.     

Synthesis and reactivity of the monomeric late-transition-metal parent amido complex [Ir(Cp*)(PMe3)(Ph)(NH2)

The late-transition-metal parent amido compound [Ir(Cp*)(PMe3)(Ph)(NH2)] (2) has been synthesized by deprotonation of the corresponding ammine complex [Ir(Cp*)(PMe3)(Ph)(NH3)][OTf] (6) with KN(SiMe3)2. An X-ray structure determination has ascertained its monomeric nature. Proton-transfer studies indicate that 2 can successfully deprotonate p-nitrophenylacetonitrile, aniline, and phenol. Crystallographic analysis has revealed that the ion pair [Ir(Cp*)(PMe3)(Ph)(NH3)][OPh] (8) exists as a hydrogen-bonded dimer in the solid state. Reactions of 2 with isocyanates and carbodiimides lead to overall insertion of the heterocumulenes into the N--H bond of the Ir-bonded amido group, demonstrating the ability of 2 to act as an efficient nucleophile. Intriguing reactivity is observed when amide 2 reacts with CO or 2,6-dimethylphenyl isocyanide. eta4-Tetramethylfulvene complexes [Ir(eta4-C5Me4CH2)(PMe3)(Ph)(L)] (L=CO (15), CNC6H3-2,6-(CH3)2 (16)) are formed in solution through displacement of the amido group by the incoming ligand followed by deprotonation of a methyl group on the Cp* ring and liberation of ammonia. Conclusive evidence for the presence of the Ir-bonded eta4-tetramethylfulvene moiety in the solid state has been provided by an X-ray diffraction study of complex 16.     

Reduction of Aldehydes and Ketones by Transition Metal Hydrides. Part 2. Reaction of trans,trans-[WH(CO)2(NO)(PMe3)2] with pyridine,functionalized aldehydes,and ketones

The reaction of trans,trans-[WH(CO)₂(NO)(PMe₃)₂] ( 1 ) with (pyridin-2-yl)-substituted aldehydes and ketones, (pyridin-2-yl)C(O)R where R = H, Me, Ph, pyridin-2-yl, and with 6-methylpyridine-2-carbaldehyde was studied. In all cases, facile insertion of the C?O bond into the W? H bond was observed, with rapid subsequent extrusionof a coordinated CO ligand affording O,N-bidentate coordinated tungsten alkoxides. Only in case of pyridine-2-carbaldehyde and di(pyridin-2-yl) ketone, the initial n¹ O-bonded insertion product could be observed as unstable intemediates by low-temperature NMR.     

Macropolyhedral boron-containing cluster chemistry. Synchrotron X-ray structural analysis of [(PMe2Ph)2Pd2B16H20(PMe2Ph)2] and [(PMe2Ph)3Pt2B16H18(PMe2Ph)]: models of intermediates to more condensed metallaboranes from the [(PMe2Ph)2PtB8H12] thermolysis system

Thermolyses of [(PMe2Ph)2PdB8H12] and [(PMe2Ph)2PtB8H12] respectively yield eighteen-vertex [(PMe2Ph)2Pd2B16H20(PMe2Ph)2] and [(PMe2Ph)3Pt2B16H18(PMe2Ph)], which exhibit structure models for probable successive precursive intermediates for the more condensed macropolyhedral metallaboranes [(PMe2Ph)4Pt3B14H16], [(PMe2Ph)2Pt2B12H16] and [(PMe2Ph)2Pt2B16H15(C6H4Me)(PMe2Ph)] that have previously been reported as products from [(PMe2Ph)2PdB8H12] thermolyses.