Bridging Fluorides and Hard/Soft Mismatch in d⁶and d⁸Complexes:  The Case of [Tl(μ-F)₃Ru(PPh₃)₃]

Abstract

[RuCl2(PPh3)3] reacts with thallium(I) fluoride to give either [Tl(mu-F)3Ru(PPh3)3] (1) or [Tl(mu3-F)(mu2-Cl)2Ru2(mu2-Cl)(mu2-F)(PPh3)4] (2) depending on the excess of TlF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)2(H2)(PPh3)3] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu3-F)(mu2-F)(mu2-X)Ru2(mu2-Br)(mu2-F)(PPh3)4] (X=Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d6 and d8 complexes containing hard ligands (such as fluoro, oxo, and amido).

A Neutral Organometallic Fluoro Complex Can Be a Good Ligand

“…Since complexes of the methallyl (2-methylallyl; h 3 -C 3 H 4 -Me-2) group are somewhat more stable than those of unsubstituted allyl, [7] and it has been our experience that phenanthroline derivatives have better crystallinity than their bipy analogues, we targeted [MoF(h 3 -C 3 H 4 -Me-2)(CO) 2 Figure 1 and Table 1). 19 F NMR spectroscopy. [9] Unlike in several previous examples, the presence of water (since the fluoride reagent is a trihydrate) did not interfere in the synthesis of 2.…”

“…Thus, it does not react with trimethylphosphine (IR and 19 F NMR monitoring, two equivalents, 5 h, room temperature). [16] Two n(CÀO) bands of similar intensity in the IR spectrum of the fluoro complex 2, due to the cis-{Mo(CO) 2 } fragment, occur at lower wavenumbers (1940 and 1858 cm [17] Since the two complexes are isostructural, these differences reflect the different properties of the two halides.…”

“…The same ™inverse halide effect∫ has been found for several families of carbonyl fluoro complexes, [1a] and has been interpreted in terms of a superior p-donor character of fluoride over the heavier halides [1a,f] in combination with four electron repulsions [18] and, more recently, as resulting from the greater ionic character of the MÀF bond. [19] Binuclear compounds: Equimolar amounts of [Mo(OTf)(h 3 -C 3 H 4 -Me-2)(CO) 2 (Figure 3 and Table 3). The cation of 3 consists of two staggered {Mo(h (4)8), [6] reflecting (2) 1.953(6) C(1)ÀO (1) 1.142(7) Mo(1)ÀC (1) 1.972(6) C(2)ÀO(2) 1.161(8) Mo(1)ÀC (3) 2.311(6) Mo(2)ÀC (21) 1.959(6) Mo(1)ÀC (4) 2.233(6) Mo(2)ÀC (22) 1.971(6) Mo(1)ÀC (5) 2.314(6) Mo(2)ÀC (24) 2.220(5) Mo(2)ÀC (23) 2.301 (5) Mo (2) …”

“…No signals attributable to the F ligands were observed in the 19 F NMR spectra of compounds 4 and 5. Similar findings have been noted previously, [1a] and were attributed to the presence of water in the solvents used.…”

“…[21] However, after several hours at room temperature, the IR and 19 F NMR data of the resulting solutions showed only the presence of the unchanged reagents, indicating insufficient lability of the triflato ligand in the group 7 complexes. Recently, we found that the triflate in [Re(OTf)(-CO) 3 (bipy)] complexes could be easily abstracted by the salt NaBAr' 4 (Ar' = 3,5-bis(trifluoromethyl)phenyl).…”