STRUCTURAL STUDIES OF STERIC EFFECTS IN PHOSPHINE COMPLEXES .5. SYNTHESIS AND CRYSTAL AND MOLECULAR-STRUCTURES OF THE DIMERS BIS(ACETATO)(TRICYCLOHEXYLPHOSPHINE)MERCURY(II) AND BIS(ACETATO)(TRI-ORTHO-TOLYLPHOSPHINE)MERCURY(II)

X-ray crystallographic studies have been carried out on two new mercury compounds containing bulky phosphine ligands [HgPCy3(OAc)2]2 (I) and [HgP(o-tol)3(OAc)2]2 (II). Crystals of I and II are monoclinic, with two dimeric molecules in each unit cell. Cell data for I are a = 9.714 (1) Å, b = 15.163 (3) Å, c = 16.686 (2) Å, 0 = 93.91 (1)°, and space group P21/c; for II the cell data are a = 10.485 (8) Å, b = 21.64 (2) Å, c = 10.762 (8) Å, π = 97.47 (5)°, and space group P21/n. For both compounds, three-dimensional intensity data were collected by four-circle diffractometer measurements and refinement was by full-matrix least-squares calculations. At convergence RF = 0.040 and RWF = 0.044 for 3181 observed reflections for I; for II the corresponding values are RF = 0.085 and RWF = 0.074 for 1398 observed reflections. The dimeric molecules are isostructural with [HgPCy3(NO3)2]2; a hitherto unknown acetato bridging mode with only one oxygen atom from each of two acetato groups linking pairs of mercury atoms is found. In both molecules, the predominant feature of the mercury coordination is the presence of three nearly coplanar strong bonds: Hg-P = 2.378 (1), Hg-O = 2.194 (5) and 2.292 (4) Å in I; Hg-P = 2.41 (1), Hg-0 = 2.36 (4) and 2.20 (4) Å in II. A fourth weaker bond (Hg-0 = 2.523 (4) Å in I and 2.73 (4) Å in II) forms the bridge to the other centrosymmetrically related mercury atom; sixfold coordination about mercury is achieved in each case by weaker intramolecular interactions with acetato oxygens (Hg-O = 2.63-2.92 A). Both compounds exist as monomers in dichloroethane solution. Cone angle calculations are made for PCy3 (θ = 179°) and P(o-tol)3 (θ = 191°) and ligand profiles are given for the bulky phosphines in I and II. © 1979, American Chemical Society. All rights reserved.