CYCLOMETALATION OF AZINE PHOSPHINES OF TYPE Z,E-PPH2CH2C(BU(T))=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)

The phosphino hydrazone Z-PPh2CH2C(Bu(t))=NNH2 1 is shown to be a covenient '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(Bu(t))=N-N=CHR [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-degrees-C to give dimethylplatinum(II) complexes [PtMe2{PPh2CH2C(Bu(t))=N-N=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 [PtMe{PPh2CH2C(Bu(t))=N-N=CH[C6H2O(OMe)2-4,6]} 4. When the dimethylplatinum(II) complex 3a was heated in toluene at 100-degrees-C, it underwent C-H bond fission with elimination of CH4 to give the cyclometallated methylplatinum(II) complex [PtMe{PPh2CH2C(Bu(t))=N-N=CH(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-degrees-C underwent oxidative addition of the C-I bond to give the cyclometallated iododimethylplatinum(IV) complex mer,cis-[PtIMe2{PPh2CH2C(Bu(t))=N-N=CH(C6-H4)}] 6a. When the bromo-mixed azine complex 3e was heated in benzene at 75-degrees-C for 16 h the cyclometallated bromodimethylplatinum(IV) complex mer,cis-[PtBrMe2{PPh2CH2C(Bu(t))=N-N=CH(C6-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 [PtMe{PPh2CH2C(Bu(t))=N-N=CH(C6H3Cl-6)}] 5d. The methylplatinum(II) complexes 5a and 5d oxidatively added Mel to give the mer,cis-iododimethylplatinum(IV) complexes 6a and 6c, respectively. Treatment of 1 with 2-carbaldehydes of pyrrole, thiophene or furan gave the corresponding phosphines 7a-7c, which with [PtMe2(cod)] at 20-degrees-C gave the dimethylplatinum(II) complexes 8a-8c, respectively. When 8a, derived from the pyrrole azine phosphine, was heated at 50-degrees-C for 10 min, the N-cyclometallated methylplatinum(II) complex [PtMe{PPh2CH2C(Bu(t))=N-N=CH(C4H3N)}] 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-degrees-C in toluene they underwent C-H bond fission to give the cyclometallated methylplatinum(II) complexes [PtMe{PPh2CH2C(Bu(t))=N-N=CH(C4H2X)}] (X = S 10a or O 10b), which oxidatively added Mel to give the iododimethylplatinum(IV) complexes mer,cis-[PtIMe2{PPh2CH2C(Bu(t))=N-N=CH(C4H2X)}] (X = S 11a or O 11b), respectively. Proton, P-31-{H-1} and some C-13-{H-1} NMR data have been obtained.