The Interplay of Methylidyne and Carbido Species: Modeling a Fundamental Step in the Fischer-Tropsch Synthesis.

Heterobimetallic μ-methylidyne complexes [WPt(μ2-CH)(CO)2L2(Tp*)], where L2 = (PPh3)2, (PPh3)(CO), (dppe), (PPh3)(CNC6H2Me3), have been obtained via the intermediacy of transient hydrido-μ-carbido complexes that undergo carbido-hydrido coupling to model a fundamental step in the proposed mechanism for Fischer-Tropsch synthesis.

Isonitrile μ-carbido complexes.

The μ-carbido complex [WPt(μ-C)Br(CO)(PPh)(Tp*)] (Tp = hydrotris(dimethylpyrazolyl)borate) undergoes substitution of one phosphine ligand with isonitriles to afford complexes [WPt(μ-C)Br(CNR)(CO)(PPh)(Tp*)] (R = Bu, CHMe-2,6, CHMe-2,4,6). For aryl but not alkyl isocyanides disubstitution follows to afford [WPt(μ-C)Br(CNR)(CO)(Tp*)] (R = CHMe-2,6, CHMe-2,4,6). The bis(isonitrile) derivatives, including [WPt(μ-C)Br(CNBu)(CO)(Tp*)], may also be prepared from the reactions of -[Pt(CNR)] with [W(CBr)(CO)(Tp*)].

Thiocarbonylphosphorane and arsorane ligands.

Independently unstable thiocarbonylphosphorane or arsorane ligands SCAR (A = P, As) are observed in the salts [W(η-,-SCAR)(CO)(Tp*)]PF [AR = PCy, PMePh: = 0, 1, 2, AsMePh; Tp* = tris(dimethylpyrazolyl)borate] which arise from the reactions of phosphonio- or arsoniocarbynes [W(≡CAR)(CO)(Tp*)] with sulfur.

Heterobimetallic μ-halocarbyne complexes.

The halocarbyne complexes [M(CX)(CO)(Tp*)] (M = Mo, W; X = Cl, Br; Tp* = hydrotris(dimethylpyrazolyl)borate) react with [AuCl(SMe)], [Pt(η-HCCH)(PPh)] or [Pt(η-nbe)] (nbe = norbornene) to furnish rare examples of μ-halocarbyne complexes [MAu(μ-CX)Cl(CO)(Tp*)], [MPt(μ-CCl)(CO)(PPh)(Tp*)] and [WPt(μ-CCl)(CO)(Tp*)]. The complex [WPt(μ-CCl)(CO)(PPh)(Tp*)] spontaneously rearranges to the μ-carbido complex [WPt(μ-C)Cl(CO)(PPh)(Tp*)] during silica-gel chromatography. One phosphine ligand of [WPt(μ-CCl)(CO)(PPh)(Tp*)] is readily substituted by CO to afford [WPt(μ-CCl)(CO)(PPh)(Tp*)].

Construction of an iminoketenylidene.

The new isonitrile-μ-carbido complexes [WPt(μ-C)Br(CNR)(PPh)(CO)(Tp*)] (R = CHMe-2,4,6, CHMe-2,6; Tp* = hydrotris(dimethylpyrazolyl)borate) rearrange irreversibly in polar solvents to provide the first examples of iminoketenylidene (CCNR) complexes.

Heterobimetallic μ-carbido complexes of platinum and tungsten.

The tungsten-platinum μ-carbido complex [WPt(μ-C)Br(CO)2(PPh3)2(Tp*)] (Tp* = hydrotris(dimethylpyrazol-1-yl)borate) undergoes facile substitution of both bromide and phosphine ligands to afford a diverse library of μ-carbido complexes that includes [WPt(μ-C)Br(CO)2(dppe)(Tp*)], [WPt(μ-C)(NCMe)(CO)2(PPh3)2(Tp*)]OTf, [WPt(μ-C)(S2CNEt2)(CO)2(PPh3)(Tp*)], [WPt(μ-C)(bipy)(CO)2(PPh3)(Tp*)]PF6, [WPt(μ-C)(phen)(CO)2(PPh3)(Tp*)]PF6, [WPt(μ-C)(terpy)(CO)2(Tp*)]PF6, [WPt(μ-C)(CO)2(PPh3)(Bp*)(Tp*)], [WPt(μ-C)(CO)2(PPh3)(Tp*)2] and [WPt(μ-C)(bipy)(CO)2(PPh3)(Bm)(Tp*)], most of which have been structurally charcaterised.

The significance of phosphoniocarbynes in halocarbyne cross-coupling reactions.

Competent intermediates in palladium(0)-copper(i) mediated catalytic cross coupling reactions of the bromocarbyne complex [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] (Tp* = hydrotris(dimethylpyrazolyl)borate) have been isolated however heterobimetallic phosphoniocarbyne complexes [WPd(μ-CPPh3)Br(CO)2(PPh3)x(Tp*)] are identified as productive (x = 1) or non-productive (x = 0) tangents to the catalytic cycle.

Tricarbonyl rhenium(i) tetrazolato and N-heterocyclic carbene complexes: versatile visible-light-mediated photoredox catalysts.

We have investigated the capacity of a range of structurally-diverse, photoactive rhenium(i) tricarbonyl complexes featuring either tetrazolato or N-heterocyclic carbene (NHC) ligands to facilitate fundamental classes of visible-light-mediated photoredox-catalysed reactions. In this study, we demonstrate that these systems mediate representative atom-transfer radical addition, hydrodehalogenation, and α-amino C-H functionalisation reactions. These rhenium(i) complexes provide greater or at least comparable reactivity to the prototypical photoredox catalyst [Ru(bpy)] in many cases.

Simple generation of a dirhodium μ-carbido complex via thiocarbonyl reduction.

The reaction of [RhCl(CS)(PPh3)2] with excess catecholborane affords the cumulenic carbido complex [Rh2(μ-C)Cl2(PPh3)4] which undergoes phosphine and halide substitution to afford a range of complexes in which the Rh[double bond, length as m-dash]C[double bond, length as m-dash]Rh spine remains intact. Amongst these, the reactions with K[L] (L = H2B(pz)2, H2B(pzMe2)2, HB(pz)3; pz = pyrazol-1-yl) afford [Rh2(μ-C)(PPh3)2(L)2] whilst with K[HB(pzMe2)3] the unsymmetrical complex [Rh2H(μ-C)(μ-C6H4PPh2-2){HB(pzMe2)3}2] is obtained in which the carbido ligand spans d6-Rh(iii) and d8-Rh(i) centres.