Fiona J. Lawlor

OXIDATIVE ADDITION OF BORON-BORON, BORON-CHLORINE AND BORON-BROMINE BONDS TO PLATINUM(0)

Abstract The synthesis and spectroscopic characterisation of the new diborane(4) compounds B2(1,2-O2C6Cl4)2 and B2(1,2-O2C6Br4)2 are reported together with the diborane(4) bis-amine adduct [B2(calix)(NHMe2)2] (calix=Butcalix[4]arene). B–B bond oxidative addition reactions between the platinum(0) compound [Pt(PPh3)2(η-C2H4)] and the diborane(4) compounds B2(1,2-S2C6H4)2, B2(1,2-O2C6Cl4)2 and B2(1,2-O2C6Br4)2 are also described which result in the platinum(II) bis-boryl complexes cis-[Pt(PPh3)2{B(1,2-S2C6H4)}2], cis-[Pt(PPh3)2{B(1,2-O2C6Cl4)}2] and cis-[Pt(PPh3)2{B(1,2-O2C6Br4)}2] respectively, the former two having been characterised by X-ray crystallography. In addition, the platinum complex [Pt(PPh3)2(η-C2H4)] reacts with XB(1,2-O2C6H4) (X=Cl, Br) affording the mono-boryl complexes trans-[PtX(PPh3)2{B(1,2-O2C6H4)}] as a result of oxidative addition of the B–X bonds to the Pt(0) centre; the chloro derivative has been characterised by X-ray crystallography.

ISOLATION AND STRUCTURAL CHARACTERIZATION OF NOVEL COMPOUNDS CONTAINING B4O2 RINGS

Two compounds containing planar six-membered B4O2 rings have been synthesized and characterized by X-ray crystallography, namely [B4O2(OH)(4)].[NH2Me2][Cl] and [B4O2(dab)(2)] (dab = 1,4-Bu-t-1,4-diazabutadiene), the former compound providing a model for one possible structure of boron monoxide. {BO}(x)

Boron–boron bond oxidative addition to rhodium(I) and iridium(I) centres

The reaction between the diborane(4) compound B2(1,2-O2C6H4)2 and either of the rhodium(I) complexes [RhCl(PPh3)3] or [{Rh(µ-Cl)(PPh3)2}2] afforded the colourless rhodium(III) bis(boryl) species [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Similar reactions have been carried out with the diborane(4) compounds B2(1,2-O2-4-ButC6H3)2, B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2, B2(1,2-O2-4-MeC6H3)2, B2(1,2-O2-3-MeOC6H3)2, B2(1,2-S2C6H4)2, B2(1,2-S2-4-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 affording analogous rhodium complexes all of which have been characterised spectroscopically. The complexes derived from the reactions with B2(1,2-O2C6H4)2 and B2(1,2-O2-3-MeC6H3)2 have also been characterised by X-ray crystallography, the structures comprising a five-co-ordinate rhodium centre with a square-based-pyramidal geometry in which the apical site is occupied by a boryl group and the phosphines are mutually trans in basal positions. Reactivity studies have also been carried out for [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Hydrolysis or alcoholysis with catechol afforded [RhH2Cl(PPh3)3] and either B2(1,2-O2C6H4)2(µ-O) or B2(1,2-O2C6H4)3 and addition of the phosphines PMe3, PEt3 and PMe2Ph afforded the new bis(boryl) compounds cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2], [RhCl(PEt3)2{B(1,2-O2C6H4)}2] and cis,mer-[RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2], the PEt3 complex having been characterised by X-ray crystallography and shown to be similar to the PPh3 complex. The iridium analogue [IrCl(PEt3)2{B(1,2-O2C6H4)}2] was also prepared from the reaction between [IrCl(PEt3)3] and B2(1,2-O2C6H4)2 and shown by X-ray crystallography to be isomorphous with the rhodium complex. Reactions between [RhCl(PPh3)2{B(1,2-O2C6H4)}2] and the phosphines PPri3, P(C6H11)3, 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2-bis(dicyclohexylphosphino)ethane (dcpe) are also described although these do not result in new rhodium boryl complexes. The reaction between [{RhCl(dppe)}2] and B2(1,2-O2C6H4)2 afforded a compound tentatively assigned as [Rh(dppe)2{B(1,2-O2C6H4)}] with analogous compounds being formed with the diborane(4) compounds B2(1,2-O2-3-MeC6H3)2 and B2(1,2-O2-4-MeC6H3)2. Finally, the reaction between [Rh(PMe3)4]Cl and the diborane(4) compound B2(1,2-O2C6H4)2 is described which affords cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2]. Analogous reactions with B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 afforded similar products.

Neutral thiolates of antimony(III) and bismuth(III)

A range of bismuth(III) and antimony(III) thiolates, Bi(SR)3(R = C6F5, 4-MeC6H4, 2,6-Me2C6H3 or 3,5-Me2C6H3) and Sb(SR)3(R = 4-MeC6H4 or 3,5-Me2C6H3) has been synthesised and the structures of the two antimony complexes have been determined. Both structures reveal a trigonal-pyramidal antimony centre bonded to three thiolate groups with, for the 4-MeC6H4 complex, additional intermolecular Sb ⋯ S interactions and, for the 3,5-Me2C6H3 complex, intermolecular arene to antimony interactions. The syntheses and structures of the organotransition-metal complexes [Bi(SC6F5){M(CO)3(η-C5H5)}2](M = Mo or W) are also reported in which the bismuth centre is bonded to one SC6F5 group and two M(CO)3(η-C5H5) fragments with no short intermolecular interactions.

Lewis-base adducts of the diborane(4) compounds B2(1,2-E2C6H4)2(E=O or S)

The reactivity of the diborane(4) compounds B 2 (1,2-E 2 C 6 H 4 ) 2 (E = O or S) have been studied with respect to their ability to co-ordinate Lewis bases, specifically 4-methylpyridine (mpy) and the phosphines PMe 2 Ph and PEt 3 . Four monoadducts have been characterised by X-ray crystallography, namely B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) and B 2 (1,2-S 2 C 6 H 4 ) 2 (PEt 3 ), together with three bis adducts B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy) 2 , B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy) 2 and B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) 2 . In the former set of compounds the one base is co-ordinated to one boron centre which adopts a tetrahedral geometry, the remaining boron being trigonal planar as in the structure of the parent compound. For the bis adducts each of the two borons is co-ordinated to a mpy or phosphine with both borons tetrahedral. Bond-length changes associated with ligand co-ordination are discussed. Multinuclear solution-state NMR studies have also been performed for solutions containing B 2 (1,2-O 2 C 6 H 4 ) 2 and mpy, B 2 (1,2-S 2 C 6 H 4 ) 2 and mpy and B 2 (1,2-S 2 C 6 H 4 ) 2 and PEt 3 . All of these studies indicate that intermolecular exchange of base between the parent compound, the mono- and the bis-adducts occurs in solution together with intramolecular exchange between the two boron centres in the monoadducts. The various rates of these processes, inasmuch as they have been determined accurately, are discussed and rationalised. The monoadducts B 2 (1,2-O/S 2 C 6 H 4 ) 2 (mpy) are nominally isoelectronic with the phenonium cation.

Co-ordination complexes of the bismuth(III) thiolate Bi(SC6F5)3

The reaction between Bi(SC6F5)31 and SPPh3 afforded crystals of [Bi(SC6F5)3(SPPh3)]5 which was characterised by X-ray crystallography. Complex 5 contains a bismuth centre bonded to three SC6F5 groups and the sulfur atom of a SPPh3 ligand such that the co-ordination geometry is disphenoidal with the SPPh3 ligand trans to one thiolate group. An additional intermolecular interaction is also present due to a weakly bridging thiolate sulfur which results in a centrosymmetric dimer with each bismuth centre having square-based pyramidal five-co-ordination. A similar structure was observed for the anion in the ionic complex [K(18-crown-6)][Bi(SC6F5)3(NCS)]6(18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) derived from the reaction between 1 and [K(18-crown-6)]SCN. The anion [Bi(SC6F5)3(NCS)]– has a disphenoidal geometry with an axial thiolate and N-bonded thiocyanate ligand which also bridges between two centrosymmetrically related bismuth centres giving a structure similar to 5. The reaction between 1 and either OPPh3, hmpa (hexamethylphosphoramide) or dmpu (N,N′-dimethylpropyleneurea) afforded the bis(ligand) complexes [Bi(SC6F5)3(OPPh3)2]·CH2Cl28, [Bi(SC6F5)3(hmpa)2]9 and [Bi(SC6F5)3(dmpu)2]10 respectively all of which were characterised by X-ray crystallography. The structures of 8–10 are all similar in being monomeric and having a five-co-ordinate, square-based pyramidal geometry around the bismuth centre with one thiolate in the apical site and the two ligands in a cis configuration in the basal plane each trans to a basal thiolate. The reaction between 1 and N,N′-dimethylthiourea, SC(NHMe)2′ afforded the tris(ligand) complex [Bi(SC6F5)3{SC(NHMe)2}3]11. An X-ray crystallographic study revealed a six-co-ordinate complex with a geometry close to that of a regular octahedron with the three thiolates and three thiourea ligands both having fac configurations. The structures are discussed in terms of the SC6F5 group having properties analogous to chloride, and hence being a pseudohalide, and also in terms of ligand co-ordination occuring through the thiolate Bi–S σ* orbitals.