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The base-catalysed addition of diphenylphosphine to the substituted diphenylethynes RC᎐ ᎐ ᎐ CRЈ (R = Ph, RЈ = Ph, o-tolyl, m-tolyl or 2-biphenyl; R = m-tolyl, RЈ = o-tolyl or m-tolyl) yielded Ph 2 PC(R)᎐ ᎐ CHRЈ and/or Ph 2 PCH(R)CH(RЈ)PPh 2 . Proton, 13 C, 13 P and two-dimensional rotating frame Overhauser enhancement 1 H NMR spectra have been used to determine the stereochemical pathways of the reactions and the stereochemistry of the products. In general the more hindered alkynes undergo monoaddition ultimately to yield phosphinoalkenes with the Ph 2 P attached to the carbon bearing the least bulky substituent and cis to the olefinic proton, while for the less hindered alkynes the trans isomer is formed initially and this then reacts further to give meso/erythro-diphosphinoalkanes. Bis(o-tolyl)ethyne does not react with Ph 2 PH under the same conditions. Crystal structures were determined for E-and Z-Ph 2 P(Ph)C᎐ ᎐ CHPh and show distortions of interbond angles consistent with the pattern of strain implied by the foregoing reactions. The sulfides of the phosphinoalkenes and the Mo(CO) 4 complexes of the diphosphinoalkanes were also prepared and their 1 H, 13 C and 31 P NMR spectra recorded. In several cases the pattern of 13 CO NMR signals for the complexes was used unambiguously to determine the stereochemistry of the parent diphosphines.

The reactivity of the double bond adjacent to the geminal diphenylphosphino groups of (Ph2P)&=CH2 facilitates the addition of species with one or more P-H bonds to provide a convenient high-yielding route to a range of new polyand ambi-dentate ligands which can form a wide variety of different types of transition metal complex.We have previously describedl the synthesis of 1,l-The presence of the double bond in (1) and its complexes bisdiphenylphosphinoethene (1) , a versatile chelating ligand

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