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The difference in reactivity towards Rh' between simple tertiary phosphines and diphenylphosphinoacetic acid can be explained by the assumption that the latter ligand, besides monodentate P bonding, tends also to react by oxidative addition of its carboxyl group, yielding P,O-chelated rhodium(itt) complexes. Crystal structures of the final product, fac-[ Rh( Ph,PCH,CO,),]~PhNO,~H,O, and of the key intermediate, mer-[ RhCI( H ) (Ph,PCH,CO,) (Ph,PCH,CO,H),]-C,H,O, were determined. The latter structure is unique in that it contains both hydride and a carboxylic proton in one molecule.

Crystal Structure of a Nickel(I1) Complex of a Chiral Bis(tertiary phosphine), Bromo[ ( R , S ) -3,6-diphenyl-3,6-diphosphaoctanedioato( 1-)][ (S,R)-3,6-diphenyl-3,6-diphosphaoctanedioic acidlnickel(I1) Hydrate The complex [NiBr(HQ)(HzQ)].H20 containing the chiral bis(tertiary phosphine), HO2CCH2(C6H,)PCH2CH2P(Cs-H5)CH2C02H (H2Q) was studied by single-crystal X-ray structural analysis. The crystal is monoclinic, P21/c, with a = 12.155 (2) A, b = 18.286 (3) A, c = 17.336 (4) A, j3 = 102.41 (1)O, and Z = 4. The structure was determined from 3065 reflections measured on a Syntex P21 diffractometer and solved and refined by conventional Patterson, Fourier, andleast-squares techniques to R = 0.046 and R, = 0.058. All atoms except four disordered methylene hydrogens were located. The central nickel atom is five-coordinated by four phosphorus atoms forming a basal plane and bromide at the top of a tetragonal pyramid. Carboxyl groups and the water molecule are not coordinated to nickel. The stereochemistry of the complex with respect to the chiral phosphorus atoms corresponds to the anti-bis(mw1igand) configuration. The two phosphine ligands are not equivalent: one of the chelate rings suffers from disorder of the methylene groups while the second adopts a normal A-skew conformation. The other difference between the ligands as follows from electroneutrality demands, Le., one being HQ-and the other HzQ, is rather formal because of extensive hydrogen bonding that counterbalances the differences between the carboxyls and constitutes a three-dimensional network holding the structure together.

CoNa(H2PO3) 3.H20, M r : 342.88, orthorhombic, Pbca, a = 9.054 (2), b = 14.706 (3), c = 14.759 (3) A, V--1965.1 (7) A 3, Z = 8, D x = 2.32, D m = 2.30 Mg m -3,/z(Mo Ka) = 2.38 mm-l; R = 0.046 (R w = 0.072) for 1980 observed counter reflections. The structure contains three crystallographically non-equivalent HPO a tetrahedra. The hydrogen bonds give rise to a three-dimensional network in which the Co and Na atoms are surrounded by octahedra of O atoms. min -1. The scanning interval was 1 °. 162 reflections were classified as unobserved [I < 1.96trl(I), where 31(I ) was derived from counting statistics]. Data were corrected for Lorentz and polarization effects and for absorption (pr --0.83). Transmission factors varied between 0.30 and 0.32. The density was determined pycnometrically in xylene at 298 K.

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