Variable coordination numbers in crystalline bis(pentamethylcyclopentadienyl)samarium oxide, iodide and alkoxide complexes

Abstract

Three crystallographically characterized organosamarium complexes containing formally {itx}-coordinate trivalent samarium have been recrystallized under appropriate conditions to give formally {itx} + 1-coordinate species. The structures of these complexes have been determined and are compared with the {itx}-coordinate structures. The implications of this structural flexibility on the steric factors which are very important in organolanthanide reactivity are discussed. Recrystallization of the seven-coordinate dihydroindenoindene diolate complex [(C{in5}Me{in5}){in2}Sm]{in2}O{in2}C{in16}H{in10} ({bd1}) from THF gives the eight-coordinate solvate [(C{in5}Me{in5}){in2}Sm(THF)]{in2}O{in2}C{in16}H{in10} ({bd2}) which crystallizes as a THF solvate in the space group {itP}2{in1}/{itn} with {ita} = 10.811(4), {itb} = 13.878(4), c = 25.114(7) \rA, \gb = 98.77(7)\dg and {itD}{incalc.} = 1.15 g cm{su\t-3} for {itZ} = 2. Least-squares refinement on the basis of 2208 observed reflections led to a final {itR} valueof 0.049. In {bd2}, two (C{in5}Me{in5}){in2}Sm bent metallocene units are coordinated to the O{in2}C{in16}H{in10} framework via SmO bonds of 2.099(9) \rA. Each Sm centre is also ligated by a THF molecule with a SmO distance of 2.490(9) \rA. Both {bd1} and {bd2} have similar O{in2}C{in16}H{in10} units but {bd2} has larger average SmC distances (2.75(2) vs 2.70(3) \rA) and a smaller (ring centroid)Sm(ring centroid) angle (132.9 vs 139.8\dg). Recrystallization of [(C{in5}Me{in5}){in2}Sm]{in2}(\gm-O) ({bd3}) from toluene in the presence of {bdCNCMe}{in3}, forms [(C{in5}Me{in5}){in2}Sm(CNCMe{in3})]{in2}(\gm-O) ({bd4}) which crystallizes in the space group {itP}2{in1}/{itc} with {ita} = 27.265(10), {itb} = 13.946(5), {itc} = 15.505(5)\rA, \gb = 101.25(3)\dg and {itD}{incalc.} = 1.28 g cm{su\t-3} for {itZ} = 4. Least-squares refinement on the basis of 8275 observed reflections led to a final {itR} value of 0.064. Like {bd3}, {bd4} has short SmO distances, 2.101(7) \rA, and a nearly linear (174.3(4)\dg) SmOSm angle. {bd4} has a larger SmC(ring) average (2.80(1) vs 2.73(1) \rA) and a smaller (ring centroid)Sm(ring centroid) angle (133.5 vs 137.2\dg). Recrystallization of (C{in5}Me{in5}){in2}SmI(THF) ({bd5}) in the presence of one equivalent of 1,5-pentamethylenetetrazole (C{in6}H{in10}N{in4}) gives the complex (C{in5}Me{in5}){in2}SmI(C{in6}H{in10}N{in4}) ({bd6}) which crystallizes in space group {itP}2{in1}/{ita} with {ita} = 15.969(10), {itb} = 10.741(10), {itc} = 17.768(7)\rA, \gb = 108.81(4)\dg and {itD}{incalc.} = 1.58 g cm{su\t-3} for {itZ} = 4. Least-squares refinement on the basis of 3327 observed reflections led to a final {itR} value of 0.061. In addition to the attachments of the two C{in5}Me{in5} rings and the iodide ligand to Sm, two of the nitrogen atoms of the tetrazole ligand are oriented towards the metal at distances of 2.539(14) and 2.812(18) \rA. The Sm(ring) average (2.73(2) \rA) in {bd6} is the same as that in {bd5} and the SmI distance is larger (3.100(2) vs 3.048(2) \rA).