Snapshots of an alkylidyne for nitride triple-bond metathesis

The transient titanium alkylidyne complex (PNP)(TiCBu)-Bu-t (PNP = N[2-P(CHMe2)(2)-4-methylphenyl](2)(-)), [2+2] cycloadds sterically bulky nitriles such as NCR to afford unique examples of kinetically stable azametallacyclobutadienes, (PNP)Ti((NCRCBu)-Bu-t) (R = Bu-t, 1; Ad, 2). Complexes 1 and 2 can further react with electrophiles such as ClSi(CH3)(3) or Al(CH3)(3) to extrude the alkyne (RCCBu)-Bu-t (R = Bu-t, 1; R = Ad, 2) and form neutral or zwitterionic titanium imide species, respectively. Imide formation for the latter species results from complete (BuC3-)-Bu-t for N3- metathetical exchange. Isotopic labeling studies applying N-15 enriched nitrile NCAd clearly reveal the nitrogen atom transfer results from incomplete and complete metathesis of a titanium alkylidyne with a nitrile.