Lawrence Barton

An approach to megalo-boranes. Mixed and multiple cluster fusions involving iridaborane and platinaborane cluster compounds. Crystal structure determinations by conventional and synchrotron methods

Abstract Several new macropolyhedral metallaboranes have been isolated from thermolytic mixed cluster fusion reactions involving metallaboranes and molten B10H14 as solvent. Co-thermolysis of B10H14 with nine-vertex [(CO)(PMe3)2HIrB8H12] (1) engenders 18-vertex [(CO)(PMe3)2IrB17H20] (3), via double cluster fusion; this has the 18-vertex configuration of syn-B18H22, but with a metal atom in the 10-position. From the same reaction, triple cluster fusion engenders 28-vertex [(PMe3)2IrB26H24Ir(CO)(PMe3)2] (4), which structurally is based on an intimate interfusion of closed 10-vertex and 12-vertex subclusters, to generate a tetrahedral tetraboron core that also has a more open commo one-boron linkage to a nido nine-vertex {IrB8} subcluster. Compound 4 exhibits interesting consequences of cluster-crevice formation and introduces the concept of globular megalo-borane structures that have borons-only cores surrounded by boron-hydride sheaths. Examination for incipient megalo-borane globular behaviour in another system, viz. [IrCl(PPh3)3] (7) with anti-B18H22, reveals a four-atom core feature in 19-vertex [(PPh3)HIrB18H18(PPh3)] (6), which has a closo-type {IrB10} 11-vertex subcluster fused to a nido 10-vertex {B10} subcluster to generate a four-atom {IrB3} tetrahedron. Examination for mixed cluster fusion in other systems reveals the generation of [(PMe2Ph)2Pt-anti-B18H20] (8), from the co-thermolysis of [(PMe2Ph)2PtB8H12] (2) and B10H14, and examination for multiple cluster fusion reveals the formation of 30-vertex [(PMe2Ph)2(PMe2C6H4)2Pt2B28H32] (10), 29-vertex [(PMe2Ph)2PtB28H32] (11) and 27-vertex [(PMe2Ph)2PtB26H26(PMe2Ph)] (12) from the same reaction. Structurally, compound 10 is based on a 10-vertex arachno-{6,9-Pt2B8} unit linked, via one B–B two-electron two-centre bond each, to two 10-vertex nido-{B10} units; it also exhibits molecular condensation in the form of two P-phenylene ortho-cycloboronations. Compound 11 is based on the 19-vertex [(PMe2Ph)2Pt-η4-anti-B18H22] configuration with an additional 10-vertex nido-{B10H13} moiety bound to the non-platinated subcluster via one B–B two-electron two-centre bond. Compound 12 is based on two nido 11-vertex {PtB10} units joined by a single commo Pt vertex, with one of these units conjoined to an arachno eight-boron unit via a two-boron common edge and an open bridging {B–H(exo)–Pt–μ-B2} link. Thermolysis of [(PMe2Ph)2PtB8H12] (2) with the pre-formed double-cluster compound anti-B18H22 generates triple-contiguity 27-vertex [(PMe2Ph)PtB26H26(PMe2Ph)] (13) which, structurally, consists of a nido 11-vertex {PtB10} unit that is fused to a second 11-vertex nido {PtB10} unit with a triangular {PtB2} face in common, and also fused to a 10-vertex nido {B10} unit with a {B2} edge in common. The sequence 12→11→10→13→4 represents a progression of increasing intimacy of cluster fusion. Small crystals of compounds 3, 11 and 12 necessitated synchrotron X-radiation for sufficient diffraction intensity.

[8,8-η2-{η2-(BH3)Ph2PCH2PPh2}-nido-8,7-RhSB9H10]: A Rhodathiaborane with a Novel Bidentate Chelating Ligand

A unique bidentate phosphane/borane ligand is present in 2, which is formed by treatment of the rhodathiaborane 1 with BH3⋅THF [Eq. (1)]. Compound 1 was prepared by the reaction of the unsaturated cluster [8,8-(PPh3)2-nido-8,7-RhSB9H10] with bis(diphenylphosphanyl)methane (dppm). The dppm–BH3 ligand in 2 coordinates to the Rh center through a P atom and a BH3 moiety, the latter by two bridging B-H-Rh bonds.

Macropolyhedral boron-containing cluster chemistry. Nineteen-vertex [S2B17H17(SMe2)]. An unusual apical boron atom of cluster connectivity six that introduces a new polyhedral borane building block

Mild thermolysis of [SB8H10(SMe2)] results in the formation of a small amount of macropolyhedral [S2B17H17(SMe2)] of which the stucture is based on the fusion, with two boron atoms in common, of a conventional nido-type eleven-vertex {SB10H9} subcluster with an unprecedented arachno-type ten-vertex {SB9H8(SMe2)} subcluster that exhibits an apical boron atom of cluster connectivity six.

Synthesis and characterization of a new dicage ortho-carborane with a supramolecular structure directed by intermolecular C-Hcarborane⋯O bonds

Abstract Reaction between [HCCCH 2 SCH(CO 2 CH 3 )] 2 ( 1 ) and the N , N -dimethylaniline adduct of decaborane(14), [{C 6 H 5 (CH 3 ) 2 N} 2 B 10 H 12 ], in refluxing toluene, affords meso -2,3-bis-(1,2-dicarba- closo -dodecaboran-1-yl-methylenethio)dimethylsuccinate, [C 2 B 10 H 11 CH 2 SCH(CO 2 CH 3 )] 2 ( 2 ). The species was characterized by spectroscopic methods and a single crystal X-ray diffraction study. The crystal structure of 2 reveals intermolecular hydrogen bonding involving the C–H unit of the carborane and the CO group of the ester function, leading to a supramolecular assembly: one-dimensional ribbons packed in zigzag fashion on the bc plane of the unit cell.

Polyhedral ruthenaborane chemistry. The ten-vertex isocloso cluster geometries of [(pcym)RuB9H9] and [(pcym)2Ru2B8H8]

Abstract [1-(pcym)-isocloso-1-RnB9H9] and [1,5-(pcym)2-isocloso-1,5-Ru2B8H8] constitute the first structurally characterised ‘clean’ monometalla and bimetalla examples of the parent ten-vertex isocloso metallaborane structural type.

Macropolyhedral boron-containing cluster chemistry. Isolation and characterisation of the 27-vertex contiguous triple-cluster species [(PMe2Ph)PtB26H26(PMe2Ph)]

Abstract Reaction between [(PMe2Ph)2PtB8H12] and anti-B18H22 in benzene results in intimate cluster fusion to generate [(PMe2Ph)PtB26H26-(PMe2Ph)] which consists of a nido eleven-vertex {PtB10} subcluster fused, with a {PtB2} triangular face in common, to a second nido eleven-vertex {PtB10} subcluster, which is fused in turn to a nido ten-vertex {B10} subcluster with a {B2} edge in common.

Macropolyhedral boron-containing cluster chemistry. Isolation and characterisation of the eighteen-vertex nido-5′-iridaoctaborano[3′,8′ : 1′,2]-closo-4-iridadodecaborane, [(CO)(PMe3)2IrB16H14Ir(CO)(PMe3)2]

The novel eighteen-vertex macropolyhedral diiridaborane [(CO)(PMe3)2IrB16H14Ir(CO)(PMe3)2] has been isolated in low yield from the products of thermolysis of the nine-vertex arachno-monoiridaborane [(CO)(PMe3)2HIrB8H12], and examined by single-crystal X-ray diffraction analysis, NMR spectroscopy and mass spectrometry. The macropolyhedral framework consists of a closo-type twelve-vetex {IrB11} subcluster and a nido-type eight-vertex {IrB7} subcluster fused with two boron atoms in common. In addition there is an iridium–boron two-electron two-centre intercluster cross-linkage that is suprafacial to the open nido subcluster. The results are briefly discussed in terms of bonding schemes among individual subclusters.

The isonido-Metalladicarbaborane [1,1,1-H{P(CH3)3}2-6-Cl-1,2,4-IrC2B8H9]

A single-crystal diffraction study of the title iridadicarbaundecaborane species, 6-chloro-1,1-bis(trimethylphosphine-P)-1-endo-H-2,3-dicarba-1-irida-isonido-undecaborane(12), [IrH(PMe3)2(C2B8H9Cl)] or [(PMe3)2(H)IrC2B8H9Cl], shows that it has an isonido-type structure with a four-membered Ir1–C2–C4–B7 open face. The presence of the chlorine substituent on vertex B6 suggests that the compound is formed via a simple ligand elimination and intrafacial addition of the metal vertex to a neighbouring boron vertex in the probable precursor compound nido-[(PMe3)2(CO)IrC2B8H10Cl].

Stoichiometric removal of ligand from phosphine-ligated copper(I) reagents with BH3.THF : a novel synthesis of di-μ-bromotetrakis(methyldiphenylphosphine)-dicopper(I) and the structures of CuBr[PMePh2]3 and {CuBr[PMePh2]2}2

Abstract Attempts to synthesize CuBr[PMePh2]2 using standard methods result in the formation of CuBr[PMePh2]3 (I). {CuBr[PMePh2]2}2 (II) has been conveniently prepared in high yield from I by the reaction with BH3 · THF in THF, and its molecular structure has been determined. {CuBr[PMePh2]2}2 (II)crystallizes in the triclinic space group P 1 with cell dimensions a = 10.362(4), b = 10.938(5), c = 12.620(6) A, α = 74.90(4), β = 67.81(3), γ = 87.91(3)° and Z = 2 (per monomeric unit). The molecule II is a dibromide-bridged dimer with two pseudo-tetrahedral copper atoms. The molecular structure of CuBr[PMePh2]3 (I) is also reported. The species crystallizes in the orthorhombic space group Pna21 with Z = 4 and cell constants a = 20.174(7), b = 10.354(3) and c = 17.267(5) A. The coordination geometry about the copper atom is approximately tetrahedral. Detailed spectroscopic data are reported for both species. This reaction involving removal of phosphines with BH3 · THF appears to be stoichiometric and general.

Functionalization of the macropolyhedral borate anion cluster [B22H22]2-: isolation and characterization of the OH and OEt derivatives

Abstract Preparation and characterization of the first derivatives of the fused macropolyhedral anion [B22H22]2− are reported. The species [B22H21OH]2− (1) and [B22H21OEt]2− (2) are obtained from workup of the products of the reaction between HgBr2 and [NBzlEt3]2[B22H22]; a cluster involving the conjoining of a closo-B12 icosahedron with a nido-B10 cluster. Washing the products with ethanol followed by thin-layer chromatography allows the isolation of 1 and 2, reproducibly, in yields of 27 and 20%, respectively. The species were characterized by NMR spectroscopy, elemental analysis and X-ray diffraction studies. The crystal structure determinations of the two species identify novel features. Apparently the influence of the O atoms in the ions [B22H21OH]2− and [B22H21OEt]2− results in the lengthening of what was a gunwale BB connection adjacent to the junction of the two cages such that the distances are 2.180 and 2.230 A, respectively. These latter are longer than the corresponding distance in the parent species [B22H22]2−, which is 2.09 A; quite long for a normal BB distance. Thus it is assumed that these B atoms, in 1 and 2, one of which bears the substituent, are not bonded to each other.