While the most common reactions of singlet methylenes are insertions into Y -H or multiple bonds, 1-3 triplet methylenes tend to abstract hydrogens from Y -H bonds. 1·2 Singlet silylenes are also known to insert,4-6 while little is known about the corresponding triplets. Several theoretical papers have been devoted to analyses of the insertions of singlet CH/-12 and SiHP-15 into a variety of bonds and the abstractions of hydrogen from H216-20 and CH417 by triplet methylene. Ab initio calculations including correlation predict that carbenes insert into Y-H9•11 ·12·15 bonds with no barrier, in agreement with the prevailing experimental evidence;1·2 however, silylene insertions may encounter significant energy barriers.