Synthesis and Reactivity of Ru(NHC)(dppp)(CO)H₂ and Ru(NHC)(dppp)(CO)HF Complexes: C–H and C–F Activation

Abstract

The hydrido fluorido ruthenium(II) complex [Ru(PPh3)(dppp)(CO)HF] [1, dppp = 1,4‐bis(diphenylphosphanyl)propane], which forms upon reaction of [Ru(PPh3)3(CO)HF] with dppp, reacts with IMes [1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene] to give the expected carbene‐containing hydrido fluorido complex [Ru(IMes)(dppp)(CO)HF] (2), as well as the C–H activated species [Ru(IMes)′(dppp)(CO)H] (3). The formation of the latter product results from the reaction of 2 with a base (IMes or Et3N). Displacement of PPh3 from [Ru(PPh3)(dppp)(CO)H2] by ICy (1,3‐dicyclohexylimidazol‐2‐ylidene) yields [Ru(ICy)(dppp)(CO)H2] (7), which upon reaction with Et3N·3HF, gives [Ru(ICy)(dppp)(CO)HF] (8). Thermolysis of 7 with C6F6 at elevated temperature generates 8 and [Ru(ICy)(dppp)(CO)(C6F5)H] (9). The related fluoroaryl complexes [Ru(ICy)(dppp)(CO)(C6F4CF3)H] (10) and [Ru(ICy)(dppp)(CO)(C5F4N)H] (11) are formed upon the room temperature C–F activation of C6F5CF3 and C5F5N by 7, but also by C–H activation of the partially fluorinated substrates p‐C6F4HCF3 and p‐C5F4HN.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Nickel fluoro complexes as intermediates in catalytic cross-coupling reactions

“…For instance, at palladium the generation of trans-[Pd(F)(4-C 5 NF 4 )(PR 3 ) 2 ] (PR 3 = PCy 3 , P i Pr 3 , i Pr 2 PCH 2 CH 2 OMe) was observed [20,51] [20,33,64]. Activation reactions at the 2-position involve reactions at nickel to yield trans-[Ni(F)(2-C 5 NF 4 )(L) 2 ] (L = PEt 3 , i Pr 2 Im), at rhodium to give [Rh(2-C 5 NF 4 )(PEt 3 ) 3 ], but also conversions at titanium and zirconium [16,19,26,28,29,52,62,66].…”

“…In general, there is a preference for the activation of pentafluoropyridine at the 4-position at a variety of transition metal complexes [20,33,51,64,65]. For instance, at palladium the generation of trans-[Pd(F)(4-C 5 NF 4 )(PR 3 ) 2 ] (PR 3 = PCy 3 , P i Pr 3 , i Pr 2 PCH 2 CH 2 OMe) was observed [20,51] [20,33,64].…”

[Ru(NHC)(P–P)(CO)HF] (NHC = N-heterocyclic carbene; P–P = xantphos, dppf) complexes: Efforts to prepare new hydrodefluorination catalysts

“…Subsequent studies revealed that substitution of the two PPh 3 ligands by the chelating phosphine dppp (1,4-bis(diphenylphosphino)propane) generated a system capable of bringing about stoichiometric CeF at the 4-position of substituted fluoroaromatics such as C 6 F 5 CF 3 [15]. In the case of partially fluorinated substrates such as C 6 F 5 H, activation of the CeF at the 4-position, as well as CeH activation, were now observed.…”

“…Synthesis of [Ru(PPh 3 )(xantphos)(CO)HF] and reaction with NHCsAs [Ru(PPh 3 )(dppp)(CO)HF] had previously been found to be a suitable precursor to [Ru(NHC)(dppp)(CO)HF][15], the xantphos analogue [Ru(PPh 3 )(xantphos)(CO)HF] (1) was prepared initially (Scheme 2). Thermolysis of [Ru(PPh 3 ) 3 (CO)HF] with 1.1 equiv of the bidentate phosphine gave 1 as a white crystalline solid, albeit in low (22%) yield.…”

Activation and Formation of Aromatic C–F Bonds

“…Whittlesey et al found ruthenium N-heterocyclic carbene (NHC) complexes are able to activate C-F bonds of hexafluorobenzene, 1,2,3,4,5-pentafluoro-6-(trifluoromethyl)-benzene, and pentafluoropyridine (Eq. 34) [70]. Notably, only N-heterocyclic carbenes bearing alkyl groups were effective in C-F activationNHCs bearing aryl groups, for example, were not active in C-F activation.…”