A reinvestigation of the reaction of Ru3(CO)~(~3-s3-P(C6H5)CH2P(C6H5)(C6H4)) (2) with carbon monoxide (Lugan, N.; Bonnet, J.-J.; Ibers, J. A. J. Am. Chem. SOC. 1985, 107, 4484-4491) under milder conditionsshows that a t room temperature 2 is in equilibrium with the adduct Ru~(CO)~~(CL~:~~-P(C~H~)CH~P-(C6H,)(C6H4)) (3a), in which one Ru-Ru bond has been broken. 3a has been isolated in 82% yield upon crystallization at -30 "C under a CO atmosphere. Similarly, 2 reacts at 0 "C with phosphines to afford compounds of general formula R U~( C O ) B L (~~-~~-P ( C B H~) C H~P ( C~H~) ( C~H~) ) (3b, L = P(C6H5)~; 3c, L = dppm). Addition of triphenylphosphine to compound 2 at 25 "C or warming a solution of 3a gives, among several compounds that have not been identified, the new dinuclear complex Ru~(CO)~(CL-?~-P(C~H~!-CH2P(C6H6)(C,H4)) (5). The nature of compounds 3a, 3b 312, and 5 has been established by spectroscopic means and for compound 3a, 3c, and 5 by X-ray diffraction methods. Crystal data: 3a, triclinic, Ct-PI, 2 = 2, a = 13.435 (2) A, b = 14.039 (2) A, c = 9.839 (2) A, a = 92.50 (l)", @ = 113.94 (l)", y = 92.86 (1)" ( t = -165 "C), final R(F) = 1.9%, NO = 5277, NV = 424; 3c, monoclinic, C&-P21/c, 2 = 4, a = 14.368 (2) A, b = 25.612 (2) A, c = 15.913 (2) A, @ = 108.09 (1)" (t = -150 "C), final R(F) = 6.8%, NO = 6301, NV = 412; 5, monoclinic, Ck-P21/c, Z = 4, a = 13.625 (3) A, b = 9.951 (2) A, c = 18.917 (4) A, @ = 97.46 (2)" (t = -155 "C), final R ( F ) = 4.8%, NO = 4404, NV = 316.