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

The regioselective addition of NEt 3, PPh 3, or pyridine to the central carbon of a cationic η 3 -allenyl/propargyl complex of platinum, {Pt(PPh 3 ) 2 (η 3 -C 3 H 3 )}(BF 4 ) ( 1 ), leads to the formation of the new cationic = NEt 3 ( 2a ), PPh 3 ( 2b ), C 5 H 5 N ( 2c )) via formation of a C−N or C−P bond, respectively. Complex 2c can transform into { cis -Pt(PPh 3 ) 2 (Py)(η 1 -CHCCH 2 )}(BF 4 ) ( 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 η 3 -allenyl/propargyl ligand. Protonation of 2b yields {Pt(PPh 3 ) 2 [η 3 -CH 2 C(PPh 3 )CH 2 ]}(BF 4 ) 2 ( 7 ). Addition of PPh 3 to a labile η 1 -allenyliridium complex, ( OC -6-42)-Ir(Cl)(PPh 3 ) 2 (OTf)(CO)(η 1 -CHCCH 2 ) ( 4 ), results in the The single-crystal X-ray structure of 5 has been determined.