Reaction of the Samarium-Hydrogen Bond in 2 with Carbon Monoxide: Formation, Isomerization, and X-ray Crystallographic Characterization of cis- and trans-((C5Me5)2Sm)2(μ-OCH=CHO)

Article abstract of DOI:10.1021/ja00292a034

<(C5Me52SmH>2 (I) reacts with CO in arene solvents to form a product, II, which generates crystals of cis-((C5Me5)2<(C6H5)3PO>Sm)2(μ-OCH=CHO) (IIIa) when (C6H5)3PO is added.IIIa crystallizes from toluene under hexane diffusion in space group P<*> with unit cell dimensions a = 18.673 (7) Angstroem, b = 17.641 (6) Angstroem, c = 13.973 (5) Angstroem, α = 102.40(3) deg, β = 93.57 (3) deg, γ = 93.15 (3) deg, and Z = 2 (with six toluene molecules of crystallization per unit cell) for D_c = 1.27 g cm^-3.Least-squares refinement on the basis of 6427 observed reflections led to a final R value of 0.065.IIIa isomerizes to the trans isomer IIIb at room temperature in hours to days depending on sample concentration.IIIb crystallizes from toluene under hexane diffusion in space group P2₁/n with unit cell dimensions a = 14.678 (2) Angstroem, b = 17,424 (3) Angstroem, c = 28.736 (4) Angstroem, β = 100.67 (1) deg, and Z = 4 for D_c = 1.34 g cm^-3.Least-squares refinement on the basis of 8312 observed reflections led to a final R value of 0.051.In both IIIa and IIIb, (C5Me5)2Sm units are connected by a bridging -OCH=CHO- moiety.The two C5Me5 ring centroids, the OPPh3 oxygen atom, and the enediolate oxygen atom describe a distorted tetrahedral coordination geometry around each samarium center.The enediolate bridge is best resolved in the cis isomer IIIa and has the following bond distances (Anstroem): Sm-O, 2.147 (10) and 2.179 (10); C-O, 1.319 (19) and 1.352 (18); C=C, 1.324 (22).O-C=C angles of 132.51 (18) deg and 128.4 (18) deg were observed.In the trans isomer IIIb there is an apparent rotational disorder of the bridging group about the Sm-O bonds.