The relationship between the structure and the properties of a drug or material is a key concept of chemistry. Knowledge of the three-dimensional structure is considered to be of such...

le] and [PtEt,( L-L)] 2a-2d affords a series of cationic platinum(ii) complexes 3a-3e which in the case of 3a-3c adopt a cis ethene/hydride ground state whereas in 3d and 3e the otherwise electron-deficient metal centre is stabilized by a two-electron, three-centre agostic interaction with the P-CH bond of the ethyl ligand. Complexes 1-3 were characterized by 'H, 13C and 31P NMR spectroscopy and for 2d and 3d by single-crystal X-ray crystallography. The influence of the chelating diphosphine ligand on the strength of the agostic bond was monitored b y NMR spectroscopy. This revealed that the cations undergo t w o fluxional processes in solution: (a) agostic methyl rotation and ( b ) 0-elimination/ethene rotation, a combination of which scrambles all five protons and both carbon atoms of the ' C, H, ' moiety. The 31P nuclei, however, remain inequivalent at temperatures u p t o 300 K.The agostic interaction was displaced by a small two-electron donor molecule L t o form the series of adducts [PtEt(L)(L-L)]+ ( L = acetonitrile or pyridine) in which the 'normal' ethyl complex is the first formed species. The adducts are unstable t o loss of C, H, by p-elimination t o form the series of cationic hydrides [PtH( L) (L-L)] +. For comparison, the complex [PtH (0,SCF,){Bu',P(CH,),PBut2}] was synthesised and characterized by H and 31P NMR spectroscopy and X-ray crystallography.104

Synthesis and Crystal and Molecular Structure of Tris-p(t-butyl isocyanide) -t r is( tbuty I isocya n ide)triangdot r i plat i nu m

Treatment of tris(norb0rnene)platinum with diphosphines and subsequent protonation affords a series of cationic complexes [Pt(C7HI1)(L2)]+ (L2 = peralkyldiphosphine) in which the norbornyl ligand binds to platinum via a-alkyl and P-C-H agostic interactions; the strength of the latter bond varies and has been characterised by n.m.r. and X-ray structure analysis.

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