Mono‐ or Diplatinum Complexes Containing a π‐Conjugated Pentadiynyl Ligand

The reaction of pentadiynyl halides XCH 2 C≡CC≡CPh ( 1 ) with equimolar amounts of Pt(C 2 H 4 )(PPh 3 ) 2 in C 6 D 6 produced cis ‐(PPh 3 ) 2 PtX(η 1 ‐CH 2 C≡CC≡CPh) ( cis ‐ 2 ) as a kinetic product. Complex cis ‐ 2 isomerized to trans ‐(PPh 3 ) 2 PtX(η 1 ‐CH 2 C≡CC≡CPh) ( trans ‐ 2 ) or trans ‐(PPh 3 ) 2 PtX[η 1 ‐C(C≡CPh)=C=CH 2 ] ( trans ‐ 3 ) under some reaction conditions. In contrast to the reaction of Pt(C 2 H 4 )(PPh 3 ) 2 , treatment of 1 with Pt(PPh 3 ) 4 generated cationic platinacyclobutene [(PPh 3 ) 2 Pt{η 2 ‐CH 2 C(PPh 3 )=C(C≡CPh)}] + Cl – ( 5 ) together with cis ‐ 2 and trans ‐ 2 . Moreover, 2 equiv. of Pt(C 2 H 4 )(PPh 3 ) 2 and 1 provided η 1 ,η 2 ‐coordinated diplatinum complex cis ‐(PPh 3 ) 2 PtCl[η 1 ‐ CH 2 C≡C{(PPh 3 ) 2 Pt(η 2 ‐C≡CPh)}] ( 7 ) and/or metallacyclobutene diplatinum complex (PPh 3 ) 2 Pt[η 2 ‐CH 2 C{(PPh 3 ) 2 PtCl}=C(C≡CPh)] ( 8 ). The coordination modes of these complexes depend on the ratio of pentadiynyl halide, Pt, and PPh 3 , as well as temperature and the nature of the solvents. Protonolysis of metallacyclobutene complexes 5 and 8 with HCl gave [ cis ‐(PPh 3 ) 2 PtCl{η 1 ‐C(C≡CPh)=C(PPh 3 )CH 3 }] + Cl – ( 9 ) and [(PPh 3 ) 2 Pt{η 3 ‐CH 2 { cis ‐(PPh 3 ) 2 PtCl}CCH(C≡CPh)}] + Cl – ( 10 ). Single‐crystal X‐ray diffraction analysis of 12 showed η 3 ‐ and η 1 ‐coordination structure.