Abstract
A bisferrocenylsilane-bridged bisphosphine, i.e., a bisphosphine bridged by bis(1’-dicyclohexylphosphino-1-ferrocenyl)dimethoxysilane, was synthesized and structurally characterized. Its redox behavior was examined by cyclic voltammetry and differential pulse voltammetry, which revealed two-step oxidation processes.
Highlights
Organic bisphosphines, i.e., organic molecules that bear two phosphine moieties as coordinating sites, represent an important class of ancillary ligands in transition-metal coordination chemistry and catalysis [1,2,3,4]
Given that the ferrocenyl group is a redox-active framework that can be modified by a variety of well-established organic synthetic methods [10,11], ferrocenyl bisphosphines could potentially serve as appropriate models for redox-controllable bisphosphine ligands [12]
Bisphosphametallocenes are potentially redox-active bisphosphine ligands given the characteristic redox behavior of the metallocene framework, and the isolation of several bisphosphametallocene derivatives has already been reported [13]. In most cases, these phosphametallocenes have only been used as simple organic bisphosphines that can chelate onto a transition metal with a relatively rigid structure based on the h5-sandwich-type skeleton, which often conceals their redox behavior
Summary
I.e., organic molecules that bear two phosphine moieties as coordinating sites, represent an important class of ancillary ligands in transition-metal coordination chemistry and catalysis [1,2,3,4]. Based on the combined consideration of the functions of both redox-active bisphosphine ligands and ferrocenylsilanes, we have designed a novel type of a redox-active bisphosphine, the two phosphine moieties of which are bridged by a bis(ferrocenyl)silene linker (Figure 1). The silyl linkage should enable electronic communication between the two 1 -biscyclohexylphosphino-1-ferrocenyl groups, and work as the redox-active bisphosphine ligand. The alkoxy groups on the silicon atom, which is bridging the redox-active moieties, should be an appropriate model. Monophosphine 1 showed a one-step oxidation wave (E1/2 = 0.30 V) at a higher potential relative to those of 2 (Figure 3b), suggesting an extended conjugation between the two ferrocenyl moieties in 2 via σ-conjugation with the Si(OMe) linker. The theoretically calculated adiabatic ionization energies for 1 (6.00 eV) and 2 (5.89 eV) suggest a lower oxidation potential for 2 relative to that of 1 [22]. FFiigguurree 44..ThTehoeroetriecatilcsaplinspdinensdietinessi(tpieusrp(lpeu) ropf l(ea)) orafd(iaca)lrcaadtiiocnal1+c,a(tbio) nrad1+ic,al(bc)atrioandi2c+a, lancdati(oc)n 2+, and (dci)cdatiicoanti2o2n+ (t2r2i+pl(ettrsiptalteet),sctaaltceu)l,actaedlcuatlathteedB3aPt Wth9e1B-D33P(WBJ)9/16--3D131(GB(J3)d/)6l-e3v1e1lGof(3thde)olreyv. el of theory
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