Tuning the Redox Potentials of Dinuclear Tungsten Oxo Complexes [(Cp*W(4,4′‐R,R‐2,2′‐bpy)(μ‐O))₂][PF₆]₂ Toward Photochemical Water Splitting

Abstract

A series of novel dinuclear tungsten(IV) oxo complexes with disubstituted 4,4'-R,R-2,2'-bipyridyl (R(2)bpy) ligands of the type [(Cp*W(R(2)bpy)(mu-O))(2)][PF(6)](2) (R=NMe(2), tBu, Me, H, Cl) was prepared by hydrolysis of the tungsten(IV) trichloro complexes [Cp*W(R(2)bpy)Cl(3)]. Cyclic voltammetry measurements for the tungsten(IV) oxo compounds provided evidence for one reversible oxidation and two reversible reductions leading to the oxidation states W(V)W(IV), W(IV)W(III) and W(III)W(III). The corresponding complexes [(Cp*W(R(2)bpy)(mu-O))(2)](n+) [PF(6)](n) (n=0 for R=Me, tBu, and 1, 3 for both R=Me) could be isolated after chemical oxidation/reduction of the tungsten(IV) oxo complexes. The crystal structures of the complexes [(Cp*W(R(2)bpy)(mu-O))(2)][BPh(4)](2) (R=NMe(2), tBu) and [(Cp*W(Me(2)bpy)(mu-O))(2)](n+)[PF(6)](n) (n=0, 1, 2, 3) show a cis geometry with a puckered W(2)O(2) four-membered ring for all compounds except [(Cp*W(Me(2)bpy)(mu-O))(2)] which displays a trans geometry with a planar W(2)O(2) ring. Examining the interaction of these novel tungsten oxo complexes with protons, we were able to show that the W(IV)W(IV) complexes [(Cp*W(R(2)bpy)(mu-O))(2)][PF(6) (-)](2) (R=NMe(2), tBu) undergo reversible protonation, while the W(III)W(III) complexes [(Cp*W(R(2)bpy)(mu-O))(2)] transfer two electrons forming the W(IV)W(IV) complex and molecular hydrogen.

Expanding the Utility of β-Diketiminate Ligands in Heavy Group VI Chemistry of Molybdenum and Tungsten

“…The bond lengths within the tungsten oxo bridges range from 1.916(4)–1.976(4) Å being substantially longer than the terminal oxo distance, 1.704(4) Å in 2 . These values are in accordance with the literature for other diamond-core μ-O,O bridged tungsten­(V) complexes. − The tungsten imido distance was found to be 1.750(5) Å, which is also in line with previously reported tungsten Dipp-imido complexes. − While the exact mechanism of the formation of complex 16 is unclear, the formation of the other crystallized reaction product can be rationalized more easily. Complex 17 is a dimeric diamond-core μ-O,O complex.…”

Synthesis and characterization of scandium complexes with reduced ligands: Crystal structures of Cp∗ScI2, [Cp∗ScI(bpy)]2, and [Cp∗ScCl(bpy)]2

“…The structure observed in 5 can be compared to those of [Cp * W(R 2 bpy)(l-O)] 2 [PF 6 ] n (R 2 bpy = 4,4 0 -R,R-2,2 0 -bipyridine; R = NMe 2 , tBu, Me; n = 0,1,2, 3) prepared by Cremer and Burger [26]. In all but one case (R = Me, n = 0), the bipyridine ligands are arranged in a cis orientation, as in 5.…”

“…The two bipyridine ligands are arranged in a cis orientation and are coplanar. A search of the CCDC database revealed numerous dimeric complexes in which two bipyridine ligands are coordinated to two transition metal centers that are bridged by two single-atom bridges, but in all but a few examples Rh 2 (g 1 -C 6 H 5 S) 2 (l-C 6 H 5 S) 2 (bpy) 2 and [Cp * W(R 2 bpy)(l-O)] 2 -[PF 6 ] n (R 2 bpy = 4,4 0 -R,R-2,2 0 -bipyridine; R = NMe 2 , tBu, Me; n = 0, 1, 2, 3) [25,26] the bipyridine ligands are in a trans orientation.…”

13 Chromium, molybdenum, and tungsten

“…H NMR shifts to the Van Vleck equation and were found to be in excellent agreement with the DFT calculations. A series of novel dinuclear tungsten(IV) oxo complexes [(Cp*W(R 2 -2,2'-bipy)(m-O)) 2 ][PF 6 ] 2 with similar disubstituted bipyridyl ligands (R ~NMe 2 , Bu t , Me, H, Cl) were prepared by hydrolysis of the corresponding tungsten(IV) trichloro complexes [Cp*W(R 2 -2,2'-bpy)Cl 3 ] 58. These complexes were examined towards the photochemical splitting of water since the redox potentials of…”