Dedicated to Professor Armin de Meijere on the occasion of his 60th birthday Group 13 difluorodiorganometalates have been known since 1955; [1] however, only a few of these were spectroscopically and structurally characterized. [2] Furthermore, the synthesis of these anions was not straightforward. We describe herein the synthesis, X-ray crystal structure, [3] and NMR and IR spectroscopic characterization of some difluorodiorganometalates [nBu 4 N][R 2 MF 2 ] (M Al, Ga, In). The synthesis of these compounds is accomplished through protonolysis of trialkyl derivatives of Group 13 metals with tetra-n-butylammonium hydrogen difluoride (TBADF) at room temperature, [4] which induces elimination of methane and addition of two fluoride ions. The compounds 1 Β± 4 are obtained as colorless, rhombic crystals (Scheme 1).
those of isoelectronic trans-[OsO 2 (CN) 4 ] 2Γ , [12,25] but also with those of the homoleptic carbonyl cations [Os(CO) 6 ] 2 [5] and, particularly, square-planar [Pt(CO) 4 ] 2 . [17,22] The new superelectrophilic [26] cation trans-[OsO 2 (CO) 4 ] 2 is unusual for two reasons:
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It is the first oxo derivative of a homoleptic metal carbonyl cation. trans-[OsO 2 (CO) 4 ] 2 joins a small but growing group of cations such as [M(CO) 5 Cl] 2 (M Rh, Ir), [27] [W(CO) 6 (FSbF 5 )] , [28] and polymeric [{Mo(CO) 4 } 2 (cis-m-F 2 SbF 4 ) 3 ] . [29] All are generated in superacids, have been structurally characterized, and have [Sb 2 F 11 ] Γ as counterion. With a number of superacidic media [1,2] and very versatile synthetic routes available, [3] it should be possible to add more cationic derivatives with the atoms N, O, or F as ligands to this list.
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trans-[OsO 2 (CO) 4 ] 2 is the first cationic metal carbonyl complex with the metal in the formal oxidation state 6. Previously the highest oxidation state of the central metal was 4. Examples include the matrix molecule [WO 2 (CO) 4 ] [20] and the pentahalo-monocarbonyl-metalate(iv) anions [PtCl 5 (CO)] Γ , [30] , [OsCl 5 (CO)] Γ , [31] and [OsF 5 (CO)] Γ . [32] Experimental Section A 50-mL glass flask fitted with a PTFE valve and a magnetic stirring bar was dried by heating in vacuo and charged with OsO 4 (0.116 g, 0.46 mmol). SbF 5 (6.34 g, 20 mmol) was added by condensation in vacuo, and the CO pressure was adjusted to 1.5 bar (3.3 mmol). The initially clear solution was vigorously stirred at room temperature. After several days the solution became turbid, and after 10 days a yellow suspension formed. At room temperature all volatile components were removed in vacuo, and a finely powdered, yellowish solid (0.612 g) was obtained. Vibrational bands observed below 800 cm Γ1 : IR: n Γ 760 (m), 704 (vs), 655 (vs), 601 (m), 490 (sh), 407 (m), 346 (m), 311 (s), 276 (s), 240 (vs); Raman: 675 (vs), 645 (m), 605 (m), 296 (s), 232 (m) cm Γ1 .