Mo(CO) 2 (PPh 3 ) 2 (O 3 SCF 3 ) 2 : Ein neuer Vorläufer einer dikationischen, metallorganischen Lewis‐Säure mit drei freien Koordinationsstellen

Organometallic Lewis Acids, LIV. — Mo(CO) 2 (PPh 3 ) 2 (O 3 SCF 3 ) 2 : A New Precursor for an Organometallic Dicationic Lewis Acid with Three Accessible Coordination Sites The reaction of Mo(CO) 2 (PPh 3 ) 2 Br 2 ( 1 ) with AgO 3 SCF 3 gives the bis(triflate) complex Mo(CO) 2 (PPh 3 ) 2 (O 3 SCF 3 ) 2 ( 3 ) which can be considered as a precursor for the 12‐e − system “Mo‐(CO) 2 (PPh 3 ) 2+ 2 ”. According to the spectroscopic data one of the two coordinated CF 3 SO − 3 anions is acting as a chelate ligand. Treatment of 3 and of the in situ generated W(CO) 2 (PPh 3 ) 2 (O 3 SCF 3 ) 2 ( 4 ) with H 2 O affords the dinuclear hydroxo‐bridged complexes [M 2 (μ‐OH) 3 (CO) 4 (PPh 3 ) 4 ][CF 3 SO 3 ] ( 5 : M = Mo; 6 : M = W). Acetonitrile replaces the CF 3 SO − 3 ligands in 3 and 4 to afford the cationic complexes [M(CO) 2 (PPh 3 ) 2 (NCMe) 3 ][CF 3 SO 3 ] 2 ( 7 : M = Mo; 8 : M = W). The reaction of 3 with an excess of 2‐butyne and 1‐phenyl‐1‐propyne leads to the monoalkyne complexes Mo(CO)(MeCCR)(PPh 3 ) 2 (O 3 SCF 3 ) 2 ( 9 : R = Me; 10 : R = Ph) in moderate yield. In contrast, the bisalkyne complexes [M(CO)(MeCCMe) 2 (PPh 3 ) 2 (O 3 SCF 3 )][CF 3 SO 3 ] ( 11 : M = Mo; 12 : M = W) are formed in high yield when a CH 2 Cl 2 solution of 2‐butyne is added to 1 and 2 in the presence of AgO 3 SCF 3 . At room temperature, 11 and 12 are highly fluxional in solution, while 9 and 10 are stereochemically rigid. Treatment of 11 with acetonitrile yields [Mo(CO)(MeCCMe) 2 (PPh 3 ) 2 (NCMe)][CF 3 SO 3 ] 2 ( 13 ). Compounds 3–13 (except 4 ) are characterized by IR, 1 H‐, 13 C‐, 19 F‐, and 31 P‐NMR spectrescopy.