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

Abstract

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.

A Dirhoda‐Heterocyclic Carbene

“…This was eventually resolved through recourse to HMBC‐ 1 H, 13 C measurements which revealed correlations between the methyl ester proton ( δ H =2.39 ppm) and μ‐alkyne carbon ( δ C =74.8 ppm) resonances. The μ‐carbido resonance was unable to be located through 1D 13 C{ 1 H} or 2D 31 P‐ 13 C{ 1 H} NMR studies owing to the low solubility of the complex in organic solvents, though it is expected to be increasingly downfield relatively to that found for [Rh 2 (μ‐ 13 C)Cl 2 (PPh 3 ) 4 ] ( δ C =424.4 ppm, 1 J RhC =47 Hz) …”

“…The signals in the 13 C{ 1 H} NMR spectrum of most interest derive from the original μ‐carbido and the added alkyne, however in the absence of 13 C‐isotopic enrichment, their identification was problematic due to their association with the six 100 % abundant I = nuclei of the 31 P 4 103 Rh 2 core. This was eventually resolved through recourse to HMBC‐ 1 H, 13 C measurements which revealed correlations between the methyl ester proton ( δ H =2.39 ppm) and μ‐alkyne carbon ( δ C =74.8 ppm) resonances.…”

Halogenation of A-frame μ-carbido complexes: synthesis of μ2-halocarbynes

“…3 The third class (C) involve a polar-covalent (dative) coordination of the terminal carbido complex [Ru(C)Cl2(PCy3)2] (1) 4 to a wide variety of metal centres, 4,5 in a manner akin to s-donor/p-acidic CO and isonitrile ligands. 5 It was recently demonstrated that one such Class B µ-carbido complex, [RuPt(µ-C)Cl4(py)2(PCy3)] (2), 4d which is obtained from 1 and trans-[PtCl2(py)2] presumably via Class C [RuPt(µ-C)Cl4(py)2(PCy3)2], reacted with bis(diphenylphosphino)methane (dppm) to afford the first example of an 'A-frame' 6 µcarbido complex [RuPt(µ-C)Cl4(dppm)2] (3) in which the octahedral d 6 -ruthenium(II) and square planar d 8 -platinum(II) centres, 7 respectively form triple and single bonds to the bridging carbido ligand (Scheme 1). This sequence constituted the first demonstration of the interconversion of two classes of µ-carbido complex (C ® B).…”

“…Synthesis of a Class B 'A-Frame' µ-Carbido complex. 4d The advent of the readily accessible symmetrical class A carbido complex [Rh2(µ-C)Cl2(PPh3)4] (4) 8 suggested to us the possibility of exploring not only symmetrical Class A A-frame µcarbido complexes but also the interconversion of carbido classes by exploiting the synthetic versatility typical of square planar d 8 -rhodium centres. We report herein both endeavours, the first of which proceeded without issue, whilst the latter afforded unprecedented access to the first examples of µ2-CCl and µ2-CBr ligands.…”

“…This is in contrast to the precursor 4 in which the two rhodium coordination planes are approximately orthogonal so as to minimise steric repulsion between (unlinked) phosphines on adjacent rhodium centres. In the absence of 13 C enrichment 8 the identification and resolution of the 15 line multiplets expected for the quaternary µ-carbido nuclei in the 13 C{ 1 H} NMR spectra of either 5a and 6 was not viable (coupling to 31 P and Scheme 2. Synthesis of Class A 'A-Frame' µ-carbido complexes.…”