Mixed Heterotri‐ to Heteropentametallic Transition‐Metal Complexes: Synthesis, Characterization and Electrochemical Behavior

The synthesis and reaction chemistry of heteromultimetallic transition‐metal complexes are discussed. Complex [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ] ( 3 ) [dppf = 1,1′‐bis(diphenylphosphanyl)ferrocene], accessible by treating [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )RuCl] ( 1 ) with equimolar amounts of HC≡C‐C 6 H 4 ‐4‐PPh 2 ( 2 ), gives on treatment with [(cod)RhCl] 2 ( 4 ), [(η 5 ‐C 5 Me 5 )RhCl 2 ] 2 ( 6 ), and [(tht)AuCl] ( 8 ) heterotrimetallic [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐{Rh}] [ 5 , {Rh} = (cod)RhCl; 7 , {Rh} = (η 5 ‐C 5 Me 5 )RhCl 2 ] and [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐AuCl] ( 9 ), respectively. Tetra‐ and even pentametallic heteronuclear complexes can be prepared by following consecutive reaction sequences: Treatment of 9 with HC≡CR { 10a , R = C 5 H 4 N‐4; 10b , R = C 6 H 4 ‐4‐C≡N; 10c , R = bpy (= 2,2′‐ b i py ridyl‐5‐yl); 12a , R = bpy[Re(CO) 3 Cl]} in the presence of HNEt 2 and [CuI] gave [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐Au‐C≡CR] { 11a , R = C 5 H 4 N‐4; 11b , R = C 6 H 4 ‐4‐C≡N; 11c , R = bpy; 13 , R = bpy[Re(CO) 3 Cl]}. Compound 11c is the key starting material for complexes of higher nuclearity. Treatment of 11c with [(nbd)Mo(CO) 4 ] ( 14 ) afforded heterotetrametallic {(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐Au‐C≡C‐bpy[Mo(CO) 4 ]} ( 15 ), whereas with [{[Ti](μ‐σ,π‐C≡CSiMe 3 ) 2 }M]X [ 16a , MX = Cu(N≡CMe)PF 6 ; 16b , MX = AgOClO 3 ] novel heteropentametallic [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐Au‐C≡C‐bpy({[Ti](μ‐σ,π‐C≡CSiMe 3 ) 2 }M)]X ( 17a , M = Cu, X = PF 6 ; 17b , M = Ag, X = ClO 4 ) is formed. The reaction of 11a with [{[Ti](μ‐σ,π‐C≡CSiMe 3 ) 2 }Cu]OTf ( 16c ) produced [(η 2 ‐dppf)(η 5 ‐C 5 H 5 )Ru‐C≡C‐C 6 H 4 ‐4‐PPh 2 ‐Au‐C≡C‐4‐C 5 H 4 N({[Ti](μ‐σ,π‐C≡CSiMe 3 ) 2 }Cu)]OTf ( 18 ). The structures of 9 , 11b , 11c , and 12 in the solid state and the electrochemical behavior of selected complexes are also reported.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)