The 13C and 119Sn NMR spectra of some four- and five-coordinate tri-n-butyltin(IV) compounds |
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Authors: | M.David Curtis Nicephoros A. Fotinos |
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Affiliation: | Department of Chemistry, The University of Michigan, Ann Arbor, MI 48109 U.S.A. |
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Abstract: | Silver tetrafluoroborate reacts with Cl(bipy)(CO)2(η3-C3H5)Mo in CH2Cl2 to give the dimeric cation, (μ-Cl)[(bipy)(CO)2(η3-C3H5)Mo]2+, isolated as the crystalline BF4? salt with CH2Cl2 of solvation (5). Complex 5 crystallizes in the triclinic system (space group P, No. 2) with cell parameters: a 11.831(2), b 10.142(3), c 15.618(3) Å; α 93.96(2), β 104.33(2), γ 91.41(2)°, V 1809.5(8) Å3Z = 2, ?calc 1.60 g cm?3. Full matrix refinement with all but three atoms anisotropic converged at R1 = 0.057 and R2 = 0.073 based on 3742 reflections with I > 30(1). The two halves of the dimer are connected by a single chloride bridge (Mo-Cl 2.554(3), 2.519(3) Å, Mo-Cl-Mo 134.0(1)°). The η3-allyl group is oriented so that its open face points toward the two cis-carbonyl groups, a feature common to all L2X(CO)2Mo(η3-allyl) structures determined to date. A molecular orbital analysis shows that this rotational preference of the allyl group has its roots in the strong π-bonding character of the carbonyls. The MO analysis also provides a rationale for regioselectivity observed in the reactions of various η3-allyl complexes with nucleophiles. In particular, the factors which determine whether the terminal carbons are attacked (giving olefin) or whether the central carbon is attacked (giving a metallacyclobutane) are exposed. |
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