Syntheses, Structures, and Reactivity of Diruthenium Phosphine Carbonyl Complexes of Nitrites and Nitrates

A series of diruthenium phosphine carbonyl complexes containing bridging nitro and nitrato groups, [Ru2(CO)4(μ-NO2)2L2] (1−4) and [Ru2(CO)4(μ-NO3)2L2] (5−9), were cleanly prepared from the reactions of [Ru2(CO)4(NCMe)4L2][BF4]2 (L = PPh3, PPh2(allyl), PPh2Me, PPhMe2, or PMe3) with excess NaNO2 or NaNO3 in MeOH. Complexes 1−4 are present in two isomeric forms, A and B, with a head-to-head orientation of two bridging η2-(N,O)-NO2 groups for form A and a head-to-tail arrangement of the groups for form B, in an approximate 3:1 ratio, but complexes 5−9 are present in only one isomeric form with an η2-(O,O)-NO3 attachment. Crystal data: 1A, a = 12.452(2) Å, b = 23.520(3) Å, c = 13.441(2) Å, β = 98.280(1)°, monoclinic P21/n, Z = 4; 5, a = 11.737(3) Å, b = 23.496(5) Å, c = 14.629(3) Å, β = 100.34(2)°, monoclinic P21/n, Z = 4. The five-membered metallacycle {Ru2(ONO)} in 5−9 is more reactive than the four-membered metallacycle {Ru2(NO)} in 1−4, reflected by the different reactivity of [Ru2(CO)4(μ-NO2)2(PPh3)2] (1) and [Ru2(CO)4(μ-NO3)2(PPh3)2] (5) with various reagents to give [Ru2(CO)4(μ-I)2(PPh3)2] (10), [Ru2(CO)4(μ-N3)2(PPh3)2] (11), and [Ru2(CO)4(η1-NO3)2(μ-X)2(PPh3)2] (X = Br (12), I (13)). Crystal data of 13: a = 31.394(3) Å, b = 9.761(1) Å, c = 18.200(2) Å, β = 118.420(1)°, monoclinic C2/c, Z = 4. The intermolecular oxygen transfer from the ligated NO2 groups in 1 to exogenous PMe3 is readily observed in MeCN at ambient temperature, apparently forming nitrosyl groups and free OPMe3.