Chromium(II) Alkoxides: Synthesis and Crystal Structure of the Monomeric 2 (R=2,6-Dimethylphenyl) and Dimeric 4 (R=Phenyl; L=THF, Pyridine) without a Cr-Cr Bond. An Insight into the Question of Cr-Cr Quadropole Bond Formation

Article abstract of DOI:10.1021/ja00188a030

Chromium(II) alkoxides have been synthesized by reaction of CrCl2THF2 with RONa .The reaction products are highly insoluble, pyrophoric, and probably polimeric <(RO)2Cr>n (1).In the case of the sterically demanding alkoxide R=2,6-(t-But)2-4-MePh, the highly soluble and monomeric (RO)2Cr(THF)2 has been obtained in crystalline form.Less bulky ligands allow a fast reaction with an excess RONa leading to the formation of the purple <(RO)4Cr>2 (2).In the case of R=2,6-dimethylphenyl, a stable crystalline compound has been isolated upon treatment with N,N,N',N'-tetramethylethylenediamine (TMEDA).The crystal data of <(2,6-Me2C6H3O)4Cr>2 (2b) at 130 K are as follows: a=13.882 (4), b=14.189 (3), c=15.700 (7) Angstroem; α=66.47 (3), β=67.99 (2), γ=87.33 (2) deg; Z=2; triclinic space group P1.Solvent removal in vacuo allows the dimerization of 2 with formation of the green <(RO)8Cr2>4 (L=THF, (py) (3).The structure of the phenyl derivative has been demonstrated by X-ray analysis.Crystal data for <(PhO)8Cr2>-4*C6H5CH3 (3a'') are as follows: a=13.672 (1), b=22.561 (1), c=23.013 (1) Angstroem; Z=4; orthorhombic space group Pccn.The long Cr...Cr distance in the complex 3a'' (3.634 (1) Angstroem) rules out the presence of a Cr-Cr bond.Na abstraction from 2 to 3 by reaction with 18-crown-6 leads to the formation of polymeric 1.