Contrasting reactions of ethylene with Os 3{μ-H,μ-OC(Me)}(CO) 10, giving an ethylene adduct, or a bis-μ-acyl complex. Crystal and molecular structure of Os 3{1,2-μ-H,1,2-μ-OC(Me)}{1-η 2-CH 2CH 2}(CO) 9

Abstract

Bubbling ethylene at atmospheric pressure through a solution of OS 3{μ-H,μ-OC(Me)}(CO) 10 ( 1) in octane at 105–110°C gives the complex Os 3{1,2-μ-H,1,2-μ-O(Me)}{1-η 2-CH 2CH 2}(CO) 9 ( 2) in 61% yield. By contrast, the bis-acyl complex Os 3{μ-OC(Me),μ-OC(Et)}(CO) 10 ( 3) is obtained in the reaction of 1 with ethylene and CO (68:1 mol ratio) at 167 atm and 140°C; an equilibrium mixture of isomers 3a (vicinal) and 3b (geminal) is obtained in which the latter predominates. Complexes 3a and 3b show an IR absorption at 1516 cm −1, characteristic of the bridging acyl group; 13C NMR for the carbon atom of this group is shifted significantly to low field, δ = 287.9 ppm. The crystal and molecular structure of 2 have been determined at 25°C using a Huber four circle diffractometer with graphite-monochromated Mo- K α radiation. Complex 2 crystallizes in the monoclinic space group P2 1/ c; cell dimensions, a = 14.423(2), b = 15.119(3), c = 17.200(3) Å, and β = 95.921(5)°; calculated density = 3.19 g cm −3. A total of 3947 unique reflections with I > 3σ( I 0) were used in the refinement; final discrepancy indices, R = 0.075 and R w = 0.087. The location of each of the six Os atoms was determined by the Patterson method. All other non-hydrogen atoms were then located by difference maps. The crystal consists of discrete molecules of complex 2 with two independent molecules in the asymmetric unit. The complex consists of three groups arrayed in a triangle, [Os(1 or 4)(η 2-CH 2CH 2)(CO) 2], [Os(2 or 5)(CO) 3] and [Os(3 or 6)(CO)4], with normal metal-metal separations, OsOs: (1)–(2) and (4)–(5) = 2.907(2) and 2.909(2) Å, (1)–(3) and (4)–(6) = 2.841(2) and 2.837(2) Å, (2)–(3) and (5)–(6) = 2.872(2) and 2.869(2) Å. A hydrogen atom and an acyl group are see n to be bridging between two of the atoms, Os(1) and Os(2) [or Os(4) and Os(5)]. It is noteworthy that the ethylene is observed to be η 2-coordinated to the same metal atom to which the oxygen of the bridging acyl group is also coordinated. The bridging hydrogen atom was located but its position not refined, Os(1)H(1) and Os(4)H(2) = 1.70 and 1.66 Å; Os(2)H(1) and Os(5)H(2) = 1.70 and 1.92 Å.