SOLID-STATE STRUCTURE OF THE TANTALUM BIS-ARYL COMPOUNDS TA(OAR-2,6-R2)3(C6H5)2 (R=ME,ISO-PR-OAR-2,6-R2=2,6-DIALKYLPHENOXIDE) - OBSERVATION OF A LACK OF CORRELATION OF M-OAR DISTANCES AND M-O-AR ANGLES FOR ARYLOXIDE DERIVATIVES OF NIOBIUM(V) AND TANTALUM(V)

Treatment of the tantalum dichloride compounds Ta(OAr-2,6Me2)3Cl2 or Ta(OAr-2,6Pr2i)3Cl2 (OAr-2,6Me2 = 2,6-dimethylphenoxide; OAr-2,6Pr2i = 2,6-diisopropylphenoxide) with phenyl lithium (2 equiv) leads to the formation of the bis-phenyl compounds Ta(OAr-2,6Me2)3(C6H5)2 (1) and Ta(OAr-2,6Pr2i)3(C6H5)2 (2), respectively, in moderate yields. Single crystal X-ray diffraction analyses of both 1 and 2 show them to be isostructural. In both compounds a trigonal bipyramidal environment about the metal centre is evident with trans, axial aryloxide oxygen atoms. Short TaO distances in the range of 1.848(5)-1.881(3) Å and almost linear TaOAr angles are present. The central coordination environments in 1 and 2 are strikingly similar to those found for the biscyclometallated compound Ta(OC6H3Ph-C6H4)2(OAr-2,6Ph2). Combining the structural data for 1 and 2 with those of other alkyl, aryloxide compounds of niobium(V) and tantalum(V) shows that the MOAr distances span a narrow range of 1.85-1.95 Å, while the corresponding MOOAr angles vary from 135 to 180° with no correlation between the two parameters. Crystal data for TaO3C36H37 (1) at 19°C: a = 19.313(3), b = 11.652(1), c = 15.288(1) Å, β = 113.13(1)°, Z = 4, dcalc = 1.446 g cm-3 in space C2/c; for TaO3C48H61 (2) at 21°C: a = 11.955(2), b = 19.585(2), c = 19.337(2) Å, β = 103.742(9)°, Z = 4, dcalc = 1.309 g cm-3 in space group P21/n. © 1990.