Vinylogue Mono‐ and Bimetallic Cationic Sesquifulvalene and Monohydro Sesquifulvalene Complexes for Second Harmonic Generation

The donor‐acceptor complexes with a vinylogue monohydro sesquifulvalene and sesquifulvalene backbone of the type [(η 5 ‐C 5 H 5 )Ru{µ‐(η 5 ‐C 5 H 4 )C 2 H 2 (η 6 ‐C 7 H 7 )}ML](PF 6 ) n [ n = 0: ML = none ( 1 ), Cr(CO) 3 ( 2 ); n = 1: ML = Ru(η 5 ‐C 5 H 5 ) ( 3a ), Ru(η 5 ‐C 5 Me 5 ) ( 3b )] and [(η 5 ‐C 5 H 5 )Ru{µ‐(η 5 ‐C 5 H 4 )C 2 H 2 (η 7 ‐C 7 H 6 )}ML](PF 6 ) n [ n = 1: ML = none ( 4 ), Cr(CO) 3 ( 5 ); n = 2: ML = Ru(η 5 ‐C 5 H 5 ) ( 6a ), Ru(η 5 ‐C 5 Me 5 ) ( 6b )], respectively, have been synthesised, and spectroscopically and structurally characterised. A charge‐shift correlation was carried out by means of 1 H NMR spectroscopic studies and an increased ground‐state donor‐acceptor interaction in the order 5 < 6b < 4 < 6a was found. The corresponding donor‐acceptor interaction in 3a and 3b varies by an insignificant amount. Hyper‐Rayleigh scattering (HRS) was applied to determine the first hyperpolarisability β of the mono‐ and dicationic complexes 3a−6b . The β values obtained for the cationic sesquifulvalene complexes 4−6b are among the largest ever measured for ruthenocenyl containing complexes due to a strong resonance enhancement: the sesquifulvalene complexes 4−6a , 6b show first hyperpolarisabilities which range between 360 and 700 × 10 −30 esu, whereas β for the monohydrosesquifulvalene complexes are considerably lower (75 and 162 × 10 −30 esu). For the latter complexes the first hyperpolarisability doubles on going from Ru(η 5 ‐C 5 Me 5 ) ( 3b ) to Ru(η 5 ‐C 5 H 5 ) ( 3a ) in the acceptor unit. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)