Regioselective addition of ammonia, primary or secondary amines, aniline, or amino derivatives either to a neutral (η 1 -allenyl)platinum complex trans-Pt(Br)(PPh 3 ) 2 (η 1 -CHCCH 2 ) (1) or to a cationic η 3 -allenyl/propargyl platinum complex [Pt(PPh 3 ) 2 (η 3 -C 3 H 3 )](BF 4 ) (2) provide the synthesis of cationic N-protonated, N-alkylated, and N-arylated η 3 -azatrimethylenemethane complexes {Pt(PPh 3 ) 2 (η 3 -CH 2 C(NRR')CH 2 ]}(X) (R=H R'=H (3a), Me (3b), Et (3c), i Pr (3d), t Bu (3e), c-C 6 H 1 1 (3f), Ph (3g), CH 2 CH 2 OH (3h), R=R'=Et (3i), c-C 3 H 6 (from azetidine 3j), Ph (3k), R=Me R'=Ph (3l); X=Br, BF 4 ), respectively. Addition of amides to 1 gave a neutral η 3 -azatrimethylenemethane complex Pt(PPh 3 ) 2 [η 3 -CH 2 C(NSO 2 Ph)CH 2 ] (4m). Similar reactions using palladium complexes yield {Pd(PPh 3 ) 2 [η 3 -CH 2 C(NRR')CH 2 ]}(X) (R=H R'= i Pr (7d), Ph (7g), R=R'=Et (7i); X=Br, BF 4 , OTf), Pd(Br)(PPh 3 )[η 3 -CH 2 C(NEt 2 )CH 2 ] (8i) and Pd(PPh 3 ) 2 [η 3 -CH 2 C(NR)CH 2 ] (R=SO 2 Ph (9m), p-SO 2 C 6 H 4 Me (9n)). Synthesis of three complexes, {M(PPh 3 ) 2 [η 3 -CH 2 C(NHR)CH 2 ]} + (M=Pt R=SO 2 Ph (3m); M=Pd R=SO 2 Ph (7m), p-SO 2 C 6 H 4 Me (7n)), can not be done by hydroamination reactions, but has been successful using protonation of η 3 -N-TMM complexes 4m, 9m, and 9n, respectively. Spectroscopic and crystallographic characterizations indicate that these N-TMM complexes exhibit intermediary structural features between η 3 -2-aminoallyl and metallacyclobutanimine complexes.We designate η 3 -O-TMM to stand for the η 3 -oxatrimethylenemethane complexes M[η 3 -CH 2 C( O)CH 2 ]; η 3 -N-TMM to stand for the η 3 -azatrimethylenemethane complexes M[η 3 -CH 2 C( NR)CH 2 ]. Accordingly, N-protonated η 3 -N-TMM complexes are referred to M[η 3 -CH 2 C(NH 2 )CH 2 ]; and N-alkylated or N-arylated η 3 -N-TMM complexes are referred to M[η 3 -CH 2 C(NHR)CH 2 ] or M[η 3 -CH 2 C(NRR')CH 2 ] (R, R'=alkyl or aryl).