Comment

Salts of the cation [(⁵-C₅Me₅)RhCl{(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]⁺ have been found to undergo intramolecular dehydrofluorinative C-C reactions on thermolysis or in the presence of a proton sponge or fluoride, to yield [{⁵,P,P-C₅Me₄CH₂C₆F₄-2-P(C₆F₅)CH₂CH₂P(C₆F₅)₂}RhCl]⁺ and then [{⁵,P,P-C₅Me₃[CH₂C₆F₄-2-P(C₆F₅)CH₂]-1,3}RhCl]⁺ (Atherton et al., 1996; Bellabarba et al., 2001). The thermolysis is dependent on the solvent and the anion. The reaction for the tetrafluoroborate salt occurs only in polar protic solvents, such as ethanol, whereas for chloride, hexafluorophosphate and tetraphenylborate salts, the reaction also occurs readily in non-polar aprotic solvents, such as benzene (Atherton et al., 1999).

The structure of [(⁵-C₅Me₅)RhCl{(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]BF₄ revealed that a tetrafluoroborate anion is positioned close to the pentamethylcyclopentadienyl ligand, such that three F atoms of the anion form a plane almost parallel (5.1° deviation) to the C₅ plane, with a separation between the two planes of ca 3.19 Å. The anion is displaced slightly from the (⁵-C₅Me₅)-Rh axis, giving rise to short FH and FC distances between the anion and the pentamethylcyclopentadienyl ligand of 2.4-2.7 and 3.1-3.3 Å, respectively (Atherton et al., 1996). A similar positioning of the anion and cation is found in the related salts [(⁵-C₅Me₅)IrCl{(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]BF₄ (Atherton et al., 1996) and [(⁵-C₅Me₅)RhCl{(C₆H₃F₂-2,6)₂PCH₂CH₂P(C₆H₃F₂-2,6)₂}]BF₄ (Fawcett et al., 1998). If BF₄^-C₅Me₅ interactions are present in aprotic solvents, then the absence of similar anionC₅Me₅ interactions in the salts of the other anions may provide the basis for an explanation for the difference in reactivity. Of particular relevance is the salt of the hexafluorophosphate anion, which is the most similar to the tetrafluoroborate anion. These two anions comprise a periphery of F atoms, with equilateral triangular faces with edges of ca 2.1-2.3 Å (Allen et al., 1987; Atherton et al., 1996; Fawcett et al., 1998). Unfortunately, crystals suitable for single-crystal X-ray diffraction studies of the non-tetrafluoroborate salts of [(⁵-C₅Me₅)RhCl{(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]⁺ have been elusive. However, the structure of the title isoelectronic ruthenium salt, [(⁵-C₅Me₅)Ru(NCMe){(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]PF₆, (I), has now been determined and is presented here.

The structure of (I) (Fig. 1) reveals that the hexafluorophosphate anion does not adopt a similar position to that of the tetrafluoroborate anion in [(⁵-C₅Me₅)RhCl{(C₆F₅)₂PCH₂CH₂P(C₆F₅)₂}]BF₄ and [(⁵-C₅Me₅)RhCl{(C₆H₃F₂-2,6)₂PCH₂CH₂P(C₆H₃F₂-2,6)₂}]BF₄. The cation shows contacts to three anions which are shorter than the sum of the van der Waals radii of the respective atoms. One anion position is close to the pentamethylcyclopentadienyl ligand, such that there is one FH distance shorter than the sum of the van der Waals radii (F36H10C = 2.626 Å). The shortest inter-ion FC(C₅Me₅) distances are between atoms F34 and C9 [3.493 (6) Å], F36 and C10 [3.564 (7) Å], and F32 and C10 [3.597 (7) Å]. However, for this anion, the shortest inter-ion FC distance of 3.028 (6) Å is between atoms F36 and C2S of the acetonitrile. The distance between atoms C3S and F36 is 3.123 (5) Å, with F36H3S2 = 2.609 Å, and that between atoms C3S and F34 is 3.396 (7) Å, with F34H3S2 = 2.481 Å.

Another anion position gives three short contacts with a C₆F₅ ring (F32F26B = 2.888 (6) Å, F32C26B = 2.964 (6) Å and F32C25B = 3.110 (6) Å) and a contact with a CH₂ H atom (F35H2A2 = 2.633 Å). The third anion position gives a contact with a C₆F₅ ring (F31C14B = 3.113 (7) Å), a CH₂ H atom (F33H1A1 = 2.599 Å) and an acetonitrile H atom (F35H3S1 = 2.428 Å).

Figure 1 A view of (I). Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.

Experimental

The title complex was obtained from the reaction of [(⁵-C₅Me₅)Ru(NCMe)₃]PF₆ with (C₆F₅)₂PCH₂CH₂P(C₆F₅)₂ in dichloromethane (10 ml) gave a yellow-green solution from which a small number of yellow crystals of (I) were obtained by cooling the reaction mixture to 273 K.

H atoms were added in idealized positions and a riding model with fixed displacement parameters [U_iso(H) = 1.2U_eq of the parent atom (1.5U_eq for methyl H atoms].

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2002); data reduction: SHELXTL (Bruker, 2001) and SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.