Chem. 53,2707Chem. 53, (1975. The crystal and molecular structures of pentane-2,4-dionato-(2,3,5,6-tetrahapto-2,3-dicarbomethoxo[2.2.~]bicycloheptadienerhodium~, Rh(C5J3702)(C7H6(C02CH3)2), have been measured by single crystal X-ray diffraction. The orange crystals are monoclinic, space group P2'/c, Z = 4, a = 9.245(4), b = 9.003(4), c = 21.680(15) A, = 113.41(5)". The calculated and observed densities are 1.645 and 1.642(5) respectively. Intensity data were collected on a Syntex P I diffractometer and a full matrix least squares refinement on 3010 observed reflections leads to a conventional R = 0.0660. The structure can be considered as a roughly square planar arrangement of ligands around the rhodium atom composed of two a-ketoenolate oxygen atoms (Rh-0, 2.037(5) and 2.025(5) A) and the centers of the two ethylenic groups. The Rh-C distances for the olefin group attached to the two carbomethoxo groups, 2.117(8), 2.108(8) A, appear to be slightly larger than those for the other olefinic group, 2.087(7), 2.082(6), and the corresponding C=C distances of 1.375 (10) . On a recueilli les donnks dYintensit6 avec un diffractometre Syntex P I et la structure affinCe par la m6thode des moindres carres (matrice complete) pour 3010 r6flexions observks a conduit a une valeur de R conventionnelle de 0.0660. On ~e u t consid6rer aue la structure com~orte en premiere approximation un arrangement plan carr6 des ligands autour deI 'atome de rhodium; cet arrangement comporte deux atomes d'oxygene du a-ckto6nolate (Rh-0,2.037(5) et 2.025(5) A) et le centre de deux groupes BthylCniques. I1 semble que les distances Rh-C (2.117(8) et 2.108(8) A) du groupe olkfinique attach6 aux deux groupes carbom6thoxo sont 16gerement plus larges que celles (2.087(7) et 2.082(6) A) de l'autre groupe ol6finique. Les distances C=C correspondantes,

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