Manganese and iron PCP pincer complexes - the influence of sterics on structure and reactivity.

The syntheses of various manganese and iron PCP pincer complexes via a solvothermal oxidative addition methodology is described. Upon reacting [Mn2(CO)10] with the ligands (P(C–Br)PCH2-iPr) (1a) and (P(C–Br)PO-iPr) (1b), Mn(I) PCP pincer complexes [Mn(PCPCH2-iPr)(CO)3] (2a) and [Mn(-PCPO-iPr)(CO)3] (2b) were obtained. Protonation of 2a with HBF4·Et2O led to the formation of [Mn(κ3P,CH,P-P(CH)PCH2-iPr)(CO)3]BF4 (3) featuring an η2-Caryl–H agostic bond. The solvothermal reaction of 1a with [Fe2(CO)9] afforded the Fe(II) PCP pincer complex [Fe(PCPCH2-iPr)(CO)2Br] (4). Treatment of 4 with Li[HBEt3] afforded the Fe(I) complex [Fe(PCPCH2-iPr)(CO)2] (5a). When using the sterically more demanding ligands (P(C–Br)PCH2-tBu) (1c) and (P(C–Br)PO-tBu)(1d) striking differences in reactivity were observed. While neither 1c nor 1d showed any reactivity towards [Mn2(CO)10], the reaction with [Fe2(CO)9] and [Fe(CO)5] led to the formation of the Fe(I) complexes [Fe(PCPCH2-tBu)(CO)2] (5b) and [Fe(PCPO-tBu)(CO)2] (5c). X-ray structures of representative complexes are provided.