Synthesis of Metallacyclobutenes of Late Transition Metals via Nucleophilic Addition of Allenyl or Propargyl Complexes

The regioselective addition of NEt3, PPh3, or pyridine to the central carbon of a cationic η3-allenyl/propargyl complex of platinum, {Pt(PPh3)2(η3-C3H3)}(BF4) (1), leads to the formation of the new cationic = NEt3 (2a), PPh3 (2b), C5H5N (2c)) via formation of a C−N or C−P bond, respectively. Complex 2c can transform into {cis-Pt(PPh3)2(Py)(η1-CHCCH2)}(BF4) (3). The reverse reaction has not been observed. It is suggested that nucleophilic addition of 1 likely involves external attack at the central carbon of the η3-allenyl/propargyl ligand. Protonation of 2b yields {Pt(PPh3)2[η3-CH2C(PPh3)CH2]}(BF4)2 (7). Addition of PPh3 to a labile η1-allenyliridium complex, (OC-6-42)-Ir(Cl)(PPh3)2(OTf)(CO)(η1-CHCCH2) (4), results in the The single-crystal X-ray structure of 5 has been determined.