Iron(0) and ruthenium(0) complexes with tridentate phosphonite ligands and their potential for ketene formation from methyl iodide, CO and a base

An efficient route to the novel tridentate phosphine ligands RP[CH2CH2CH2P(OR′)2]2 (I: R = Ph; R′ = i-Pr; II: R = Cy; R′ = i-Pr; III: R = Ph; R′ = Me and IV: R = Cy; R′ = Me) has been developed. The corresponding ruthenium and iron dicarbonyl complexes M(triphos)(CO)2 (1: M = Ru; triphos = I; 2: M = Ru; triphos = II; 3: M = Ru; triphos = III; 4: M = Ru; triphos = IV; 5: M = Fe; triphos = I; 6: M = Fe; triphos = II; 7: M = Fe; triphos = III and 8: M = Fe; triphos = IV) have been prepared and fully characterized. The structures of 1, 3 and 5 have been established by X-ray diffraction studies. The oxidative addition of MeI to 1–8 produces a mixture of the corresponding isomeric octahedral cationic complexes mer,trans-(13a–20a) and mer,cis-[M(Me)(triphos)(CO)2]I (13b–20b) (M = Ru, Fe; triphos = I–IV). The structures of 13a and 20a (as the tetraphenylborate salt (21)) have been verified by X-ray diffraction studies. The oxidative addition of other alkyl iodides (EtI, i-PrI and n-PrI) to 1–8 did not afford the corresponding alkyl metal complexes and rather the cationic octahedral iodo complexes mer,cis-[M(I)(triphos)(CO)2]I (22–29) (M = Ru, Fe; triphos = I–IV) were produced. Complexes 22–29 could also be obtained by the addition of a stoichiometric amount of I2 to 1–8. The structure of 22 has been verified by an X-ray diffraction study. Reaction of 13a/b–20a/b with CO afforded the acetyl complexes mer,trans-[M(COMe)(triphos)(CO)2]I, 30–37, respectively (M = Ru, Fe; triphos = I–IV). The ruthenium acetyl complexes 30–33 reacted slowly with 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) even in boiling acetonitrile. Under the same conditions, the deprotonation reactions of the iron acetyl complexes 34–37 were completed within 24–40 h to afford the corresponding zero valent complexes 5–8. It was not possible to observe the intermediate ketene complexes. Tracing of the released ketene was attempted by deprotonation studies on the labelled species mer,trans-[Fe(COCD3)(triphos)(CO)2]I (38) and mer,trans-[Fe(13COMe)(triphos)(CO)2]I (39).