Transition metal dicarbollide complexes: synthesis, molecular, crystal and electronic structures of [M(C2B9H11)(NMe2)3] (M = Nb or Ta) and their insertion reactions with CO2 and CS2 †

Abstract

The homoleptic amides [M(NMe 2 ) 5 ] (M = Nb 1 or Ta 2; the latter is characterised by a structural study) reacted with the carborane nido-C 2 B 9 H 13 to eliminate two equivalents of HNMe 2 and generate the dicarbollide half-sandwich tris(dimethylamide) complexes [M(C 2 B 9 H 11 )(NMe 2 ) 3 ] (M = Nb 3 or Ta 4). The crystal structures of isomorphous 3 and 4 have been determined and reveal two NMe 2 ligands in a vertical orientation and the third one in a horizontal orientation with respect to the η 5 -co-ordinated face of the C 2 B 9 H 11 ligand. The electronic factors responsible for the amide ligand orientations in these complexes are explored using qualitative MO arguments. Complexes 3 and 4 reacted with CO 2 and CS 2 to yield the tris(carbamateor Ta 8) complexes, respectively. The crystal structures of 6 and 7 show two (dithio)carbamate ligands in horizontal and one in vertical orientation, demonstrating the similarity between the σ,π-donor frontier orbitals of the ligands NMe 2 and X 2 CNMe 2 in 4 and 6 or 7 respectively.

First structural characterisation of a 2,1,12-MC2B9 metallacarborane, [2,2,2-(NMe2)3-closo-2,1,12-TaC2B9H11]. Trends in boron NMR shifts on replacing a {BH} vertex with a metal {MLn} vertex in icosahedral carboranes

“…1 (C), 2 (B) and 3 (A), boron data have been assigned here for the first time and are listed in Table 1. As these three TaC 2 B 9 cages are shown to have closo geometries by X-ray diffraction, 23 it is possible to compare the differences in the boron chemical shifts caused by replacing a boron vertex with a metal vertex in the three closo-C 2 B 10 H 12 isomers. Average shift differences of ϩ8.9 ppm (max./min.…”

Tetrakis(dimethylamido)vanadium(IV)

“…Within the large family of complexes with secondary amido ligands of the type NR 2 (where R is a hydrocarbyl or other non-H group), the simplest are the mononuclear homoleptic dimethylamido species [M(NMe 2 ) n ] (n = 4, 5 or 6). The following members of this family have been crystallographically characterized: [Nb(NMe 2 ) 5 ] (Heath & Hursthouse, 1971), [Ta(NMe 2 ) 5 ] (Batsanov et al, 1999), [Mo(NMe 2 ) 4 ] (Chisholm et al, 1978), [Mo(NMe 2 ) 6 ] (Chisholm et al, 1987) and [W(NMe 2 ) 6 ] (Bradley et al, 1969). Tetrakis(dimethylamido)zirconium, usually referred to as a four-coordinate species,`[Zr(NMe 2 ) 4 ]', actually adopts the NMe 2 -bridged dimeric structure [Zr 2 ("-NMe 2 ) 2 (NMe 2 ) 6 ] in the solid state (Chisholm et al, 1988).…”

Insertion and cleavage reactions of [closo-3,1,2-Ta(NMe2)3(C2B9H11)] with nitriles, phenols and thiols; structural characterisation of N,N-dimethylamidinate ligands †

“…We recently reported the synthesis and characterisation of the dicarbollide tris(dimethylamide) [closo-3,1,2-M(NMe 2 ) 3 -(C 2 B 9 H 11 )] (M ᎐ ᎐ Nb, 1 or Ta 2), together with the insertion of CO 2 and CS 2 into the M-NMe 2 bonds of 1 and 2 to give tris(carbamate) and tris(dithiocarbamate) complexes. 1 These are rare examples of dicarbollide complexes with Group 5 metals, 2,3 and of complexes containing both dicarbollide and amide ligands. 4 The amminolysis reaction of metal amides with acids is well known, 5 and in recent years has found use as a novel method for ligand co-ordination, 6,7 occasionally providing routes to otherwise inaccessible compounds 8 or thermodynamic product ratios.…”

“…1 H NMR (500 MHz, CD 2 Cl 2 ): δ 3.20 (s, 3 H, NMe) 3.12 (s, 6 H, 2 × NMe),3.06 (s, 6 H, 2 × NMe), 3.04 (s, 3 H, NMe) 2.90 (s, 2 H, carborane C-H), 2.31 (s, 3 H, C-Me) and 2.21 (s, 6 H, C-Me). Additional peaks in 1 H-{ 11 B} NMR (CD 2 Cl 2 ): δ 2.77 (1 H), 2.14 (2 H), 2.02 (2 H), 1.85 (1 H) and 1.69 (3 H).…”