Polyhedral platinaborane chemistry. Some structural and NMR studies on the four-vertex arachno-1-platinatetraborane system

Abstract

The structure of the four-vertex platinaborane [1,1-(PPh 3) 2-arachno-1-PtB 3H 7] ( 4) has been determined from single-crystal X-ray diffraction data and compared to the disordered asymmetric structure of the compound [1,1-(PMe 2Ph) 2- arachno-1-PtB 3H 7] ( 1) and to the palladium analogue [1,-(1,1′-bdppf)-l-PdB 3H 7] ( 3) (bdppf=bis(diphenylphosphino)ferrocene). Compound 4 crystallizes in the triclinic space group P 1 , with a=1065.2(2), b=1800.6(3), c=989.0(2) pm, α=99.14(2), β=108.23(1), γ=88.06(1)°, Z=2 and V=1.7785(5) nm 3; R=0.045 ( R w=0.091). The B(2)Pt(1)B(4) plane of the borane ligand is slightly tilted (7.7(4)°) with respect to the platinum-bis(phosphorus) plane and resembles the arrangement found in the dimethylphenylphosphine compound it and the palladium analogue 3. NMR properties of compound 4 have been measured and those of compound 1 remeasured and reassessed. In both compounds 1 and 4 the nucleus of the platinum atom is more strongly coupled to that of the central boron atom ( 1 j 195pt 13C) c. 600 Hz) compared to those of the outer boron atoms ( 1 J( 195Pt- 11B) c. 230 Hz). This is in contrast to the coupling pattern found for 1 J( 165pt- 13C) in π- allyl η 3-C 3H 5-type compounds, suggesting that the central boron atom may be bound to the platinum atom via a bond with substantial 2-electron 2-centre s character.