Synthesis of Monocarbollide Complexes of Rhodium

Abstract

The compounds [RhX(PPh 3 ) 3 ] react with nido-7-NH 2 Bu t -7-CB 10 H 12 in toluene to give the 16-electron complexes [RhX(PPh 3 )(η 5 -7-NH 2 Bu t -7-CB 10 H 10 )] (1a, X ) Br; 1b, X ) Cl). The structure of the zwitterionic molecule 1a was determined by X-ray crystallography. Crystals are monoclinic, space group P2 1 /c, with a ) 12.937(3) Å, b ) 18.101(4) Å, c ) 14.695(4) Å, β )104.21(2)°, and Z ) 4. The metal atom is coordinated on one side by Br and PPh 3 groups and on the other in the pentahapto manner by the open CBBBB face of the cage system. Reactions of the complexes with several donor molecules have been investigated. With CNBu t , by changing the stoichiometry or work-up procedures either the 18-electron complexes [RhX(CNBu t )(PPh 3 )(η 5 -7-NH 2 Bu t -7-CB 10 H 10 )] (2a, X ) Br; 2b, X ) Cl) or [Rh(CNBu t ) 2 (PPh 3 )(η 5 -7-NHBu t -7-CB 10 H 10 )] (3) are obtained, or the 16-electron complex [Rh(CNBu t )(PPh 3 )(η 5 -7-NHBu t -7-CB 10 H 10 )] ( 4) is formed. Formation of 3 and 4, in which the rhodium atoms are ligated by a nido-7-NHBu t -7-CB 10 H 10 cage, formally a 3 π-electron donor, is unusual and results from loss of HX from the precursors 1. To establish firmly the nature of these species, their molecular structures were determined by X-ray crystallography. Crystals of 3 are monoclinic, space group P2 1 /c, with a ) 10.533( 2) Å, b ) 19.110(4) Å, c ) 19.707(4) Å, β )105.413(9)°, and Z ) 4, while those of 4 are triclinic, space group P1 h, with a ) 9.840(3) Å, b ) 10.809(3) Å, c ) 17.287(3) Å, R ) 88.49(2)°, β ) 84.57(2)°, γ ) 69.809( 14)°, and Z ) 2. The two molecular structures are very similar: the rhodium atom is attached on one side via an η 5 -bonding mode to the open face of the 7-NHBu t -7-CB 10 H 10 cage and on the other by the PPh 3 ligand and one or two CNBu t molecules, respectively. The reactions between the compounds 1 and PEt 3 , PMe 3 , NC 5 H 4 Me-4, and tetrahydrofuran (thf) give the complexes [RhBr(PEt 3 )(η 5 -7-NH 2 Bu t -7-CB 10 H 10 )] ( 5), [RhCl(PMe 3 ) 2 (η 5 -7-NH 2 -Bu t -7-CB 10 H 10 )] ( 6), and [RhBr(L)(η 5 -7-NH 2 Bu t -7-CB 10 H 10 )] (7a, L ) NC 5 H 4 Me-4; 7b, L ) thf), respectively. Prolonged refluxing of mixtures of [CoCl(PPh 3 ) 3 ] and nido-7-NH 2 Bu t -7-CB 10 H 12 in toluene gives the arene-(carborane)-cobalt complex [Co(η 6 -C 6 H 5 Me)(η 5 -7-NHBu t -7-CB 10 H 10 )] (8), the structure of which was determined by X-ray diffraction. Crystals are monoclinic, space group P2 1 /c, with a ) 16.332(5) Å, b ) 10.397(2) Å, c ) 22.186(6) Å, β )102.94(2)°, and Z ) 8. NMR data for the new compounds are reported and discussed in relation to their structures. † The compounds described in this paper have a rhodium atom incorporated into a closo-1-carba-2-rhodadodecaborane structure. However, to avoid a complicated nomenclature for the complexes reported, and to relate them to the many known rhodium species with η 5 -coordinated cyclopentadienyl ligands, we treat the cages as nido-11-vertex ligands with numbering as for an icosahedron from which the twelfth vertex has ...

Amine–nitrile coupling in amino-monocarbollide complexes of molybdenum

“…Recently in our laboratories, it was shown that the carbaborane 7-NH 2 Bu t -nido-7-CB 10 H 12 reacts with [RhCl-(PPh 3 ) 3 ] in refluxing toluene to give 16-electron [1-NH 2 Bu t -2-Cl-2-PPh 3 -closo-2,1-RhCB 10 H 10 ]. 9 This contrasts with the earlier work of Hawthorne et al, in which the non-N-substituted carbaborane 7-NH 3 -nido-7-CB 10 H 12 was found to react with the same rhodium reagent in methanolic KOH solution to give the anion [1-NH 2 -2,2-(PPh 3 ) 2 -2-H-closo-2,1-RhCB 10 H 10 ] Ϫ . 10 Significantly, the latter rhodium-carbaborane complex, upon mild thermolysis, forms dimeric [2,2Ј-µ-H-{1,2Ј-µ-NH 2 -2-PPh 3closo-2,1-RhCB 10 H 10 } 2 ] Ϫ , in which each of the µ-NH 2 units forms a bridge between the cage-carbon atom of one {RhCB 10 } cluster and the rhodium centre of the other.…”

Metal Complexes of Monocarbon Carboranes: A Neglected Area?

“…Although much of the group's initial work with 11-vertex monocarborane ligands involved metal-phosphine fragments, [23] it is only very recently that such moieties have been incorporated into complexes with the smaller monocarboranes. Of particular interest were the products obtained by reaction of the [closo-1-CB 8 H 9 ] À anion with fM(PEt 3 ) 2 g nþ cations (M=Rh, n ¼ 1; M=Pt, n ¼ 2).…”

Metal complexes of monocarbon carboranes bearing C-amine or -amino substituents

“…Thus the compounds [RhX(PPh 3 ) 3 ] react with 7-NH 2 Bu t -nido-7-CB 10 H 12 in toluene to give the 16-electron zwitterionic Rh III complexes [1-NH 2 Bu t -2-X-2-PPh 3 -closo-2,1-RhCB 10 H 10 ] (3a, X = Cl; 3b, X = Br) [16]. The structure of 3b was confirmed by X-ray diffraction analysis, which showed that the rhodium is coordinated on one side by Br and PPh 3 groups and on the other in the pentahapto manner by the open CBBBB face of the carborane ligand.…”

“…In contrast with the reactions of the compounds [RhX(PPh 3 ) 3 ] with 7-NH 2 Bu t -nido-7-CB 10 H 12 that yielded 3a,b, the cobalt reagent [CoCl(PPh 3 ) 3 ] only reacted after prolonged refluxing for several hours in toluene, unexpectedly yielding the 18-electron arenecobalt complex [1-NHBu t -2-(g 6 -C 6 H 5 Me)-closo-2, 1-CoCB 10 H 10 ] (11a) [16]. Formation of 11a prompted an investigation as to whether other structurally similar arene-rhodium compounds could be obtained from the reagent 3a.…”