1,2-bis(dimethylamino)ethane complexes of heteroleptic alkylzinc compounds: Correlation between Zn-N distance and R-Zn-R' bond angle

The synthesis and isolation of heteroleptic diorganylzinc compounds enforces the use of either sterically demanding substituents or the formation of a tmeda complex. The occupation of the coordination sites at the zinc atom prevents the dismutation to the homoleptic derivatives. These tmeda adducts show a linear dependency of the R-Zn-R' bond angle and the Zn-N distance, which is discussed in detail for two examples. Zn-N bond lengths of 215 pm and a C-Zn-Cl angle of 122.2 degrees are observed for [1,2-bis(dimethylamino)ethane-N,N']zinc chloride phenyl(trimethylsilyl)methanide (triclinic, P (1) over bar, a = 974.9(3), b = 985.2(3), c = 1262.6(3) pm, alpha = 67.35(2)degrees, beta = 78.42(2)degrees, gamma = 63.02(2)degrees, Z = 2), whereas the substitution of the chlorine substituent by a methyl group (triclinic, P (1) over bar, a = 974.74(8), b = 998.03(8), c = 1276.21(9) pm, alpha = 67.492(5)degrees, beta = 77.880(6)degrees, gamma = 63.291(5)degrees, Z = 2) leads to a Zn-N bond length of 224 pm with a widened C-Zn-C angle of 131.1 degrees. The extrapolation of the linear relation predicts a Zn-N distance of 290 pm for a linear R-Zn-R' moiety, a bond length of 190 pm for an angle of 109 degrees. This last mentioned value corresponds to a Zn-N single bond such as, for example, in the heteroleptic tris(trimethylsilyl)methylzinc bis(trimethylsilyl)amide (monoclinic, P2(1)/n, a = 904.74(7), b = 1668.72(9), c = 1806.76(8) pm, beta = 94.670(5)degrees, Z = 4) with a value of 184.6 pm.