Reactivity of terminal imido complexes of group 4-6 metals: stoichiometric and catalytic reactions involving cycloaddition with unsaturated organic molecules

Imido complexes of early transition metals are key intermediates in the synthesis of many nitrogen-containing organic compounds. The metal-nitrogen double bond of the imido moiety undergoes [2+2] cycloaddition reactions with various unsaturated organic molecules to form new nitrogen-carbon and nitrogen-heteroatom bonds. This review article focuses on reactivity of the terminal imido complexes of Group 4-6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination, alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.

Synthesis, molecular and electronic structure, and reactions of a Zn-Hg-Zn bonded complex

Reaction of ((Ar')NacNac)ZnI with potassium/mercury amalgam gave the trimetallic compound {((Ar')NacNac)Zn}2Hg (1) containing a Zn-Hg-Zn unit and the first example of a bond between two different Group 12 metals; DFT and QTAIM analyses suggest that 1 is best described as two formally Zn(I) atoms with a Hg(0) atom positioned between them; reactions of 1 with stoichiometric I2, FpI or Fp2 gave addition products of the type ((Ar')NacNac)ZnX (X = I, Fp) and Hg. (Ar')NacNac = HC{C(Me)N(2,6-C6H3(i)Pr2)}2; Fp = CpFe(CO)2.

Synthesis and Characterization of (2,4,6-Trimethylphenylimido)molybdenum Complexes. X-ray Crystal Structures of (L(OEt))Mo(Nmes)(2)Cl, (L(OEt))Mo(Nmes)Cl(2), and MoCl(3)(Nmes)(depe) (mes = 2,4,6-Trimethylphenyl, L(OEt) = (eta-C(5)H(5))Co{P(O)(OEt)(2)}(3), depe = Et(2)PCH(2)CH(2)PEt(2))

The bis(imido) complex MoCl(2)(Nmes)(2)(dme) (1) (mes = 2,4,6-trimethylphenyl, dme = 1,2-dimethoxyethane) has been used as the starting material for the preparation of the compounds (L(OEt))Mo(Nmes)(2)Cl (2) (L(OEt) = (eta-C(5)H(5))Co{P(O)(OEt)(2)}(3)) and Mo(Nmes)(2)(acac)(2) (5), as well as for the synthesis of the mixed oxo-imido MoCl(2)(Nmes)(O)(dme) (6), the latter reaction involving conproportionation of 1 and MoCl(2)(O)(2)(dme). Similarly, the paramagnetic mono(imido) species Mo(Nmes)Cl(3)(dme) (11) can also be obtained from 1 by interaction with MoCl(4)(THF)(2) (THF = tetrahydrofuran) in refluxing dme. Compounds 6 and 11 are suitable sources for the synthesis of other diamagnetic mixed oxo-imido and paramagnetic mono(imido) compounds, respectively. Three of the newly synthesized complexes, namely, (L(OEt))Mo(Nmes)(2)Cl (2), (L(OEt))Mo(Nmes)Cl(2) (12), and MoCl(3)(Nmes)(depe) (14) (depe = Et(2)PCH(2)CH(2)PEt(2)) have been characterized by X-ray crystallography.