Preparative and N.M.R. studies of polyphosphorus ligands and their complexes

Singh Nandha, Balbir (1992) Preparative and N.M.R. studies of polyphosphorus ligands and their complexes. Doctoral thesis, City of London Polytechnic.


A wide range of diphosphines and their complexes with chromium, molybdenum, and tungsten carbonyl moieties has been synthesised and characterised, arid studied by proton, C-13 and P-31 n.m.r. spectroscopy. In many cases the diphosphines have one or more centres of chirality, and this leads to the formation of diastereomers that are readily distinguishable by n.m.r. The P-31 chemical shifts occur in specific ranges that are often structurally diagnostic, and are interpreted in terms of 'group contributions’, 'coordination chemical shifts', and the effects of chelate 'ring strain’.

In order to obtain values of geminal and vicinal P-31 to proton coupling constants which can be used to assess conformational details, recourse was had to C-13/H -1 two-dimensional heteronuclear chemical shift correlation experiments. These use effective chemical shifts introduced by the presence of a single C -13 nucleus to reduce the extent of second-order character in the spectrum and hence give values of N(PC) and N(PH) together with their relative signs.

Synthetic studies have also been undertaken on the triphosphine ligand (Ph2P)2CHCH2PPhH, which has a chiral phosphorus atom, and its complexes. When all three phosphorus atoms are coordinated to the same metal atom this leads to considerable ring strain, but nonetheless such complexes are stable, but show interesting variations in their n.m.r. properties. The presence of the P-H bond in this triphosphine and its complexes permits base-catalysed addition reactions with species such as (Ph2P2)2C=CH2 to yield derivatives of the pentaphoshine [(Ph2P)2CHCH2]2PPh in a regio- and even stereo-selective manner. This behaviour has been studied, and several new complexes have been prepared and their n.m.r. properties have been determined.

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