Polyhedral osmaborane chemistry: the platination of [4,4,4-(CO)(PPh3)2-nido-4-OsB5H9] and the isolation, nuclear magnetic resonance properties, and molecular structures of two seven-vertex nido-type dimetallaheptaboranes [(CO)(PPh3)2HOs(PMe2Ph)ClPtB5H7] and [(CO)(PPh3)(PPh2)Os(PPh3)PtB5H7Ph]

Abstract

Reaction of the nido six-vertex osmaborane [(CO)(PPh₃)₂OsB₅H₉]1 with base followed by [PtCl₂(PMe₂Ph)₂] yields (34%) the air-stable lemon-yellow seven-vertex osmaplatinaborane [(CO)(PPh₃)₂[graphic omitted]tB₅H₇]2 which retains the approximate structure of the nido six-vertex osmaborane 1, but which has three basal atoms (BBOs) co-ordinated trihapto to a {PtCl(PMe₂Ph)} moiety, with the platinum and osmium atoms linked by a two-electron hydrogen bridge. The overall seven-vertex structure resembles that of a regular triangulated dodecahedron that has a five-connected vertex missing. It is geometrically and electronically nido. Treatment of this species with base, or thermolysis at 140°C, gives a small yield (3%) of the related species [(CO)(PPh₃)([graphic omitted]tB₅H₇Ph]3. This is formally derived from 2via PPh₃⇌ PMe₂Ph ligand exchange plus the elimination of HCl, and has a similar nido-type seven-vertex osmaplatinaheptaborane cluster geometry. Now however there is a direct osmium–platinum bond, the metals are also linked by a four-electron {PPh₂} bridge, and a migrant phenyl group is bound to a basal boron atom on the nido-{OsB₅} subcluster. The compounds have been investigated by NMR spectroscopy, the results of which suggest that a number of other (minor) products from the reactions may also be interesting platinaosmaboranes. Crystals of 2 are monoclinic, space group P2₁/n, with a= 1.5397(3), b= 1.8489(3), c= 1.7189(3) nm, β= 92.568(13)° and Z= 4. Crystals of 3 are triclinic, space group P(no. 2), with a= 1.4491(7), b= 1.7730(4), c= 1.0763(3) nm, α= 82.08(2), β= 102.71(3), γ= 105.42(4)° and Z= 2.