Preparation of Pyrazole–Pyrazolate Half‐Sandwich Complexes of Ruthenium and Osmium

Pyrazole (HRpz) [MCl(η 6 ‐p ‐cymene)(HRpz)L]BPh 4 ( 1 – 8 ) and imidazole (HIm) complexes [MCl(η 6 ‐p ‐cymene)(HIm)L]BPh 4 ( 9 – 10 ) [M = Ru, Os; R = H, 3‐Me, 3,5‐Me 2 ; L = P(OEt) 3 , PPh(OEt) 2 , PPh 2 OEt, CN t Bu] were prepared by allowing the dichloro compounds MCl 2 (η 6 ‐p ‐cymene)L to react with the appropriate azole in the presence of NaBPh 4 . Treatment of the dichloro complexes with an excess of both pyrazole and NEt 3 yielded the pyrazole–pyrazolate derivatives [M(Rpz)(η 6 ‐p ‐cymene)(HRpz)L]BPh 4 ( 11 – 14 ). Conversely, the reaction of carbonyl compounds RuCl 2 (η 6 ‐p ‐cymene)(CO) with pyrazole or imidazole yielded the bisazole complexes [MCl(η 6 ‐p ‐cymene)(HRpz) 2 ]BPh 4 or [MCl(η 6 ‐p ‐cymene)(HIm) 2 ]BPh 4 ( 15 – 17 ). The complexes were characterised spectroscopically (IR and 1 H, 13 C, 31 P NMR) and by X‐ray crystal structure analysis [RuCl(η 6 ‐p ‐cymene)(HRpz){PPh(OEt) 2 }]BPh 4 ( 1b ), [Ru(pz)(η 6 ‐p ‐cymene)(HRpz){P(OEt) 3 }]BPh 4 ( 11a ) and [RuCl(η 6 ‐p ‐cymene)(HRpz) 2 ]BPh 4 ( 15 ).