CLOSO-MONOCARBABORANES AS LIGANDS FOR TRANSITION-METALS - SYNTHESIS AND REACTIVITY OF EXO-DIPHOSPHINEPLATINUM-CLOSO-MONOCARBABORANE COMPLEXES, STRUCTURE OF [PT(BUT2P(CH2)2PBUT2)(CLOSO-CB11H12)][CB11H12]

Protonation of the complexes [PtR2(L-L)] [R = Me, L-L = (C6H11)2P(CH2)3P(C6H11)2 1a; Bu2(t)P(CH2)3PBu2(t), 1b; Bu2(t)P(CH2)1PBu2t 1c; or Bu2(t)PCH2C6H4CH2PBu2(t), 1d; R = CH2Bu(t), L-L = (C6H11)2P(CH2)3P(C6H11)2, 2a; Bu2(t)P(CH2)3PBu2t, 2b; or Bu(t)2P(CH2)2PBu(t)2, 2c] with the monocarbaborane acid HCB11H12 in diethyl ether at 0-degrees-C affords the exo-diphosphineplatinum-closo-monocarbaborane complexes [Pt(L-L)(closo-CB11H12)][CB11H12] [L-L = (C6H11)2P(CH2)3P(C6H11)2, 3a, Bu(t)2P(CH2)3PBu(t)2, 3b; Bu(t)2P(CH2)2PBu(t)2 3c; or Bu(t)2PCH2C6H4CH2PBu(t)2, 3d] in which the coordinated closo-CB11H12 ligand is strongly bound to platinum via two exo-polyhedral three-centre two-electron (Pt...H...B) bridges. These complexes are fluxional in solution at room temperature. A single-crystal X-ray diffraction study of 3c confirmed the bonding mode of the dodecarborane ligand. Complex 3c crystallizes in the monoclinic space group C2/c, a = 16.199(4), b = 16.564(5), c = 14.896(3) angstrom, beta = 93.64(2)-degrees and Z = 4. The final discrepancy index was R = 0.043, R' = 0.050 for 2838 independent reflections. The geometry around the platinum centre is distorted square planar with mu-H-Pt 1.90(8), Pt-B 2.342(8) and B-mu-H 1.23(8) angstrom. In contrast when the solvent is changed from ether to tetrahydrofuran (thf), complex 1b on protonation is converted into [PtMe(thf){Bu(t)2P-P(CH2)3PBu(t)2}][CB11H12] 5. Complexes 3b-3d react with acetonitrile to yield [Pt(NCMe)2(L-L)]-[CB11H12]2[L-L = Bu(t)2P(CH2)3PBu(t)2, 6b; Bu(t)2P(CH2)2PBu(t)2, 6c; or Bu(t)2CH2C6H4CH2Bu(t)2, 6d]. Likewise 3b reacts with pyridine affording [Pt(NC5H5)2{Bu(t)2P(CH2)3PBu(t)2}][CB11H12]2 7. However C2H4, CO and PPh3 do not react readily with these complexes. The thf complex 5 reacts with deuteriated acetonitrile to form [PtMe(NCCD3){Bu(t)2P(CH2)3PBu(t)2}][CB11H12] 8. Spectroscopic data for the new complexes are presented and discussed.