Generation and Reactions of Ruthenium Phosphido Complexes [(η5‐C5H5)Ru(PR′3)2(PR2)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions

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Abstract
Reactions of [(η5‐C5H5)Ru(PR′3)2(Cl)] with NaBArF [BArF−=B{3,5‐[C6H3(CF3)2]}4−; PR′3=PEt3 or 1/2Et2PCH2CH2PEt2 (depe)] and PR2H (R=Ph, a; tBu, b; Cy, c) in C6H5F, or of related cationic Ru(N2) complexes with PR2H in C6H5F, gave the secondary phosphine complexes [(η5‐C5H5)Ru(PR′3)2(PR2H)]+ BArF− (PR′3=PEt3, 3 a–c; 1/2depe, 4 a,b) in 65–91 % yields. Additions of tBuOK (3 a, 4 a; [D6]acetone) or NaN(SiMe3)2 (3 b,c, 4 b; [D8]THF) gave the title complexes [(η5‐C5H5)Ru(PEt3)2(PR2)] (5 a–c) and [(η5‐C5H5)Ru(depe)(PR2)] (6 a,b) in high spectroscopic yields. These complexes were rapidly oxidized in air; with 5 a, [(η5‐C5H5)Ru(PEt3)2{P(O)Ph2}] was isolated (>99 %). The reaction of 5 a and elemental selenium yielded [(η5‐C5H5)Ru(PEt3)2{P(Se)Ph2}] (70 %); selenides from 5 c and 6 a were characterized in situ. Competitive deprotonation reactions showed that 5 a is more basic than the rhenium analog [(η5‐C5H5)Re(NO)(PPh3)(PPh2)], and that 6 b is more basic than PtBu3 and P(iPrNCH2CH2)3N. The latter is one of the most basic trivalent phosphorus compounds [pKa(acetonitrile) 33.6]. Complexes 5 a–c and 6 b are effective ligands for Pd(OAc)2‐catalyzed Suzuki coupling reactions: 6 b gave a catalyst nearly as active as the benchmark organophosphine PtBu3; 5 a, with a less bulky and electron‐rich PR2 moiety, gave a less active catalyst. The reaction of 5 a and [(η3‐C3H5)Pd(NCPh)2]+ BF4− gave the bridging phosphido complex [(η5‐C5H5)Ru(PEt3)2(PPh2)Pd(NCPh)(η3‐C3H5)]+ BArF− in approximately 90 % purity. The crystal structure of 4 a is described, as well as substitution reactions of 3 b and 4 b.

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