ORGANOTRANSITION-METAL COMPLEXES OF MULTIDENTATE LIGANDS .10. STERIC VS ELECTRONIC CONTROL ON FORMATION OF 6-COORDINATE AND 7-COORDINATE CARBONYL HALIDES OF MOLYBDENUM(II) AND TUNGSTEN(II)

Halogenation of the complexes (N-N)M(CO)4 gives either the six- or seven-coordinate compounds (N-N)M(CO)mX2 (N-N = H2CPz2, H2CPz’2, H2CPz”2, PhHCPz2, or PhHCPz’2; Pz = pyrazol-1-yl; Pz’ = 3,5-dimethylpyrazol-1-yl; Pz” = 3,4,5-trimethylpyrazol-1-yl; = Mo or W; m = 2 or 3; X = Br or I). Formation of these stable carbonyl halides with one specific coordination number is explainable in terms of the interplay of the steric and electronic effects. The explanation is further supported by the structural details of the crystal structures of the paramagnetic compounds (H2CPz’2)Mo(CO)2Br2 (2) and (PhHCPz’2)Mo(CO)2I2 (9) and the diamagnetic compound (H2CPz”2)W(CO)3Br2 (7). 2: triclinic; PĪ; a = 8.198 (2) Å, b = 9.130 (3) Å, c = 12.291 (4) Å; α = 81.57 (2)°, β = 89.50 (2)°, γ = 83.94 (2)°; V = 905.0 (5) Å3; Z = 2; ρ = 1.894 g cm-3; R = 0.033, Rw = 0.031 based on 1619 reflections with I > 2.5σ(I). 7: monoclinic; P21/c; a = 13.255 (5) Å, b = 9.956 (4) Å, c = 16.315 (7) Å; β = 109.28 (4)°; V = 2032.2 (14) Å3; Z = 4; ρ = 2.157 g cm-3; R = 0.047, Rw = 0.051 based on 1803 reflections with I > 3.0σ(I). 9: orthorhombic; Pnma; a = 16.438 (4) Å, b = 14.600 (4) Å, c = 9.515 (3) Å; V = 2283.5 (11) Å3; z = 4; ρ = 1.996 g cm-3; R = 0.037, Rw = 0.040 based on 1426 reflections with I > 3σ(7). © 1990, American Chemical Society. All rights reserved.