CYCLOMETALATION OF 2-HALOGENOBENZALDEHYDE MIXED AZINE PHOSPHINES OF TYPE PPH2CH2C(TBU)=N-N=CH(C6H4X-2) (X=1, BR OR CL) INVOLVING FACILE C-XBOND FISSION AT TUNGSTEN(0)

Condensation of Z-PPh2CH2C(tBu)=NNH2 with 2-halobenzaldehydes gave mix ed azines of the type ZE-PPh2CH2C((tBu)=N-N=CH(C6H4X-2) (X = I, 2a; Br , 2b; Cl, 2c; or F, 2e, respectively). 2a, 2b, or 2c reacted with fac- [W(CO)3(NCEt)3 to give tungsten(0) complexes [W(CO)3(NCEt){PPh2CH2C(tB u)=N-N=CH(C6H4X-2)}] (3a-3c), which rapidly underwent oxidative additi on to give seven-coordinate tungsten(II) complexes of the type [WX(CO) 3{PPh2CH2C(tBu)=N-N=CH(C6H4)}] (4a-4c). The fluoro-mixed azine Ph2PCH2 C(tBu)=N-N=CH(C6H4F-2) (2e) with fac-[W(CO)3(NCEt)3] gave [W(CO)3(NCEt ){PPh2CH2C(tBu) =N-N=CH(C6H4F-2)}] (3e) which did not undergo C-F oxid ative addition, but when treated with CO or CN(t)Bu gave tungsten(0) c omplexes of the type [W(CO)3L{PPh2CH2C(tBu)=N-N=(C6H4F-2)}] (L=CO, 5a or CN(t)Bu, 5b). The mixed azine from 2-chloro-6-fluorobenzaldehyde an d 1 ie. PPh2CH2C(tBu)=N-N=CH(C6H3Cl-2,-F-6) (2d) with fac-[W(CO)3(NCEt )3] underwent oxidative addition at the C-Cl bond to give [WCl(CO)3{PP h2Ch2C(tBu)=N-N=CH(C6H3F-6)}] (4d) via a tungsten(0) complex 3d. Treat ment of the aryl-tungsten(II) complex [WBr(CO)3{PPh2CH2C(tBu)=N-N=CH(C 6H4)}] (4b) with NaBH4/CO Caused aryl-tungsten bond fission (reductive elimination) and C=N reduction to give the benzylhydrazone-phosphine complex [W(CO)4(PPh2 CH2C(tBu)=NNHCH2Ph}] (6) which was also formed by reducing the benzaldehyde mixed azine phosphine tungsten(0) complex [ W(CO)4{PPh2CH2C(tBu)=N-N=CHPh}] (8) with NaBH4.