Molybdenum bis(imide) complexes of the general formula (DME)Cl2Mo(NR)2 catalytically metathesize acyclic imine substrates. This CN bond-forming reaction has significant implications for the synthesis of small molecules by ring-closing metathesis and polymers by ring-opening metathesis. A series of closely related NR transfer reactions were examined in an effort to fully understand the process. (RO)2Mo(CHR‘)(NAr) (1a, Ar = 2,6-diisopropylphenyl in all cases; R = C(CF3)2CH3) underwent alkylidene/imine exchange with a variety of imines in situ to give a mixed bis(imide) product and an olefin. The reactivity decreased if the alkoxide substituents were changed for more electron donating ones. (DME)Cl2Mo(NR)2 (3a, R = 2,6-diisopropylphenyl; 4, R = t-Bu) reacted with imines in an imide/imine metathesis to give mixed bis(imide) complexes and new imines. The reaction rates depended strongly on the steric demands of the imide NR substituent. Replacement of the chlorides with more electron donating alkoxide ligands inhibited the reactions. Compounds 3a and 4 also exchanged imide ligands with each other (imide/imide metathesis). Finally, compounds 3a and 4 were found to catalytically metathesize mixtures of two imines at 80 °C in 105 and 22 h, respectively. It was established that the reaction is mediated by the presence of unique initiation products in catalytic mixtures. A catalytic cycle is proposed and the nature of the mechanism is discussed in terms of the data gathered on all of the metatheses.

Mixtures of (n-Pr)NdCHPh ( 3) and PhNdCH-(t-Bu) (4) undergo catalytic metathesis in the presence of 4 mol % of (DME)Cl 2 Mo(dNR) 2 (R ) t-Bu (1a), 2,6diisopropylphenyl ( 2)) at 85-90 °C in C 6 D 6 to form 1:1: 1:1 equilibrium mixtures with PhNdCHPh ( 5) and (n-Pr)NdCH(t-Bu) (6).

dme)Cl 2 Mo(=NAr) 2 + PhN=CHBu t (dme)Cl 2 Mo(=NAr)(=NPh) + ArN=CHBu t 1 2 3 4

Pyrroline, a five-membered cyclic imine, undergoes ring-opening metathesis with alkylidene complexes of the class Mo(CHR‘)(NAr)(OR)2 (Ar = 2,6 diisopropylphenyl; R = CMe3, CMe2(CF3), CMe(CF3)2; R‘ = CMe3, CPhMe2). An intermediate pyrroline-bound complex was isolated and characterized crystallographically for the R = CMe2(CF3) derivative. This adduct, Mo(CHBut)(NAr)[OCMe2(CF3)]2[pyrroline], transforms to the mixed bis(imide) product, Mo(NCH2CH2CH2CHCHBut)(NAr)[OMe2(CF3)]2, with a first-order rate constant of 1.4 × 10-2 min-1 at 55 °C. The reaction of the R = CMe3 derivative produces not only the ring-opened product but also a byproduct, Mo[CH(CMe2Ph)(C4H8N)](O)(NAr)(OBut).

Mo(CH-t-Bu)(NAr)[OCMe2(CF3)]2 (1, Ar = 2,6 diisopropylphenyl) undergoes ring-opening metathesis with pyrroline (C4H7N) to give the mixed bis(imide) product Mo(NCH2CH2CH2CHCH-t-Bu)(NAr)[OMe2(CF3)]2 (2). An intermediate N-bound pyrroline adduct Mo(CH-t-Bu)(NAr)[OCMe2(CF3)]2[pyrroline], 3, was isolated and characterized spectroscopically and by X-ray diffraction.