Cyclometallation of azine phosphines of type Z,E-PPh2CH2C(But)N–NCHR (R = an aromatic or heterocyclic group) involving X–Y (X = C, N or O; Y = H, I or Br) bond fission by platinum(II)

Abstract

The phosphino hydrazone Z-PPh2CH2C(But)NNH21 is shown to be a convenient ‘reagent’ for converting aryl or heterocyclic aldehydes into azines which can then be cycloplatinated readily with C–H, C–I, C–Br, N–H or O–H bond fission. Condensation of 1 with benzaldehyde derivatives (RCHO) gave mixed azines of type Z,E-PPh2CH2C(But)N–NCHR [R = Ph 2a, C6H2(OMe)3-3,4,5 2b, C6H4NO2-4 2c, C6H4I-2 2d, C6H4Br-2 2e, C6H4Cl-2 2f or C6H2(OH-2)(OMe)2-4,6 2g]. The azines 2a–2f reacted with [PtMe2(cod)](cod = cycloocta-1,5-diene) at 20 °C to give dimethylplatinum(II) complexes [[graphic omitted]CHR}]3a–3f respectively, containing six-membered chelate rings. Treatment of 2g with [PtMe2(cod)] effected O–H bond fission to give the O-cyclometallated methylplatinum(II) complex [[graphic omitted](OMe)2-4,6]}]4. When the dimethylplatinum(II) complex 3a was heated in toluene at 100 °C, it underwent C–H bond fission with elimination of CH4 to give the cyclometallated methylplatinum(II) complex [[graphic omitted]C6H4)}]5a. Similarly, 3b and 3c were converted into the corresponding cyclometallated methylplatinum(II) complexes 5b and 5c, respectively. The square-planar dimethylplatinum(II) complex 3d in benzene at 20 °C underwent oxidative addition of the C–I bond to give the cyclometallated iododimethylplatinum(IV) complex mer,cis-[[graphic omitted]H4)}]6a. When the bromo-mixed azine complex 3e was heated in benzene at 75 °C for 16 h the cyclometallated bromodimethylplatinum(IV) complex mer,cis-[[graphic omitted]H4)}]6b formed. In contrast the chloro-mixed azine complex 3f underwent the C–H bond fission and not C–Cl bond fission to give the cyclometallated square-planar methylplatinum(II) complex [[graphic omitted]H3Cl-6)}]5d. The methylplatinum(II) complexes 5a and 5d oxidatively added Mel to give the mer,cis-iododimethylplatinum(IV) complexes 6a and 6c, respectely. Treatment of 1 with 2-carbaldehydes of pyrrole, thiophene or furan gave the corresponding phosphines 7a–7c, which with [PtMe2(cod)] at 20 °C gave the dimethylplatinum(II) complexes 8a–8c, respectively. When 8a, derived from the pyrrole azine phosphine, was heated at 50 °C for 10 min, the N-cyclometallated methylplatinum(II) complex [[graphic omitted])}]9 and methane were formed via a N–H bond fission. When the dimethylplatinum(II) complexes 8b or 8c, derived from the thiophene or furan azine phosphines, were heated at 100 °C in toluene they underwent C–H bond fission to give the cyclometallated methylplatinum(II) complexes [[graphic omitted]H2X)}](X = S 10a or O 10b), which oxidatively added Mel to give the iododimethylplatinum(IV) complexes mer,cis-[[graphic omitted]H2X)}](X = S 11a or O 11b), respectively. Proton, 31P-{1H} and some 13C-{1H} NMR data have been obtained.