Alcohol Exchange and Oxidation Reactions of Doubly Bonded Ditungsten(IV) Complexes of the Type W2Cl4(OR)4(ROH)2: The Structural Identification of Novel Hydrogen-Bonded Bridging Systems

Article abstract of DOI:10.1021/ja00348a023

The alcohol/alkoxide exchange reactions of W2Cl4(μ-OR)2(OR)2(ROH)2 with R'OH have been studied.When R = C2H5 and R' is a primary alkyl group, complete exchange occurs to give W2Cl4(μ-OR')2(OR')2(R'OH)2 with R' = n-C3H7, n-C4H9, i-C4H9, n-C5H11, and n-C8H17.When R' is a secondary alkyl group, only partial exchange occurs to give W2Cl4(μ-OC2H5)2(OR')2(R'OH)2, with R' = 2-C3H7, 2-C4H9, and 3-C5H11.The compound W2Cl4(μ-O-i-C3H7)2(O-i-C3H7)2(i-C3H7OH)2 can be prepared by reaction of WCl4 with i-C3H7OH.The proton NMR spectra of all of these compounds plus several others previously reported show that when the R groups in the nonbridging OR and ROH ligands are primary, OH proton exchange with free ROH is rapid, whereas when R is secondary, such exchande is slow on the NMR time scale.Three compounds with secondary R groups have been studied by X-ray crystallography: 1, W2Cl4(μ-OC2H5)2(O-i-C3H7)2(i-C3H7OH)2; 2, W2Cl4(μ-O-i-C3H7)2(O-i-C3H7)2(i-C3H7OH)2; 3, W2Cl4(μ-OC2H5)2(O-3-C5H11)2(3-C5H11OH)2. 1 crystallizes in space group Cmmm with a = 11.882(2) Angstroem, b = 16.919(3) Angstroem, c = 14.406(5) Angstroem, and Z = 4.There are two independent molecules resident on positions of mmm (D_2h) symmetry, and some disorder in the μ-OC2H5 group occurs. 2 crystallizes in space group P2₁/c with a = 14.190(5) Angstroem, b = 13.715(6) Angstroem, c = 15.509(7) Angstroem, β = 99.71(3) deg, and Z = 4.There are two independent molecules, each residing on an inversion center. 3 crystallizes in space group P1/ with a = 10.459(3) Angstroem, b = 11.205(3) Angstroem, c = 17.280(4) Angstroem, α = 92.76(3) deg, β = 111.96(2) deg, γ = 105.62(2) deg, Z = 2.There are two crystallographically independent molecules residing on inversion centers.In 1 the W-O_T bond lengths within each molecule appear to be equal, which would imply that the ROHOR hydrogen bonds are symmetrical.In 2 and 3 there are small inequalities.The possible influence of crystalline environment on the symmetry of the ROHOR bridging units is discussed.