Molybdenum alkylidyne complexes that contain a 3,3 '-di-t-butyl-5,5 ',6,6 '-tetramethyl-1,1 '-biphenyl-2,2 '-diolate ([Biphen](2-)) ligand

The reaction between K-2[Biphen] ([Biphen](2-) = 3,3'-Di-t-butyl-5,5',6,6'-tetramethyl-1,1'-Biphenyl-2,2'-diolate) and Mo(NArCl)(CH-t-Bu)(OTf)(2)(dme) (Ar-Cl = 2,6-Cl2C6H3) in the presence of ten equivalents of triethylamine gave Mo(NHArCl)(C-t-Bu)[Biphen] (4a) in 40-50% yield. Addition of K-2[S-Biphen] to Mo(NArCl)(CHCMe2Ph)(OTf)(2)(THF) in THF led to the isolation of Mo(NHArCl)(CCMe2Ph)[S-Biphen] (4b) in similar to40% yield. An X-ray crystal study of 4b confirmed the proposed structure and also revealed that one ortho chloride approaches within 2.93 Angstrom of the metal approximately trans to the alkylidyne ligand. Addition of one equivalent of H-2[Biphen] to Mo(CCH2SiMe3)[N(i-Pr)Ar)](3) (Ar = 3,5-dimethylphenyl) produced Mo(CCH2SiMe3)[Biphen][N(i-Pr)Ar)] in situ, which when treated with one equivalent of 1-adamantanol gave a mixture of Mo(CCH2SiMe3)[Biphen](OAd) (9) and three equivalents of HN(i-Pr)Ar, from which 9 could be isolated as a beige powder in 46% yield. An X-ray study of 9 confirmed that it is a pseudotetrahedral species in which the ModropC bond length is 1.707(15) Angstrom and the ModropC-C angle is 168.3(11)degrees. Addition of ten equivalents of 2-butyne or 3-hexyne to a pale yellow solution of 9 produced the molybdacyclobutadiene complexes Mo(C3R3)[Biphen](OAd) (R = Me or Et; 10a and 10b, respectively) in high yield. Both 10a and 10b decompose slowly in solution, even in the presence of added alkyne. An X-ray structure of the decomposition product of 10a revealed it to have the stoichiometry of 10a plus one additional equivalent of 2-butyne. The most unusual feature of the structure of this alkyne complex is a fusion of the C3Me3 portion of the metallacyclobutadiene ring to carbons in position 5 and 6 in the [Biphen](2-) backbone to create a sigma allyl linkage. These results suggest that Mo biphenolate alkylidyne complexes are not likely to be stable under conditions where alkynes are metathesized. (C) 2003 Elsevier B.V. All rights reserved.