Acetylene/Vinylidene Rearrangements of Fe(CO) 2 L 2 (silylacetylene) Complexes (L=Phosphorus Donor)

The reaction of a mixture of Fe(CO) 2 (PEt 3 ) 2 N 2 ( 1a ) and [Fe‐(CO) 2 (PEt 3 ) 2 ] 2 N 2 ( 1b ) with acetylene leads to three complexes: Fe(CO) 2 (PEt 3 ) 2 (π‐HC≡CH) ( 2a ), Fe(CO) 2 (PEt 3 ) 2 (H)(C≡CH) ( 2b ), and Fe(CO) 2 (PEt 3 ) 2 CCH 2 ( 2c ). Upon chromatography on silylated silica gel the mixture of 2a‐c is completely transformed into 2c . The analogous reaction of 1a, b or of Fe(CO) 2 [P(O i Pr) 3 ] 2 N 2 ( 1d ) with HC≡CSiMe 3 affords the primary oxidative addition products Fe(CO) 2 L 2 (H)(C≡CSiMe 3 ) [L PEt 3 , 3a ; L P(O i Pr) 3 , 3c ]. The presence of a small amount of Al 2 O 3 in hexane irreversibly converts 3a and 3c into the vinylidene compounds Fe(CO) 2 L 2 CC(H)SiMe 3 [L PEt 3 , 4a ; L P(O i Pr) 3 , 4c ]. The chromatographic work‐up of 4c additionally leads to the hydrolysis product Fe(CO) 2 [P(O i Pr 3 ) 2 ] 2 CCH 2 ( 2d ). The reaction of the phosphite‐substituted derivative Fe(CO) 2 [P(OMe) 3 ] 2 I ‐ ( 1c ) with silylacetylene allows detection of the acetylene species Fe(CO) 2 [ P(OMe) 3 ] 2 (HC ≡CSiMe 3 ) ( 3b ), as well as the acetylido hydrido derivative Fe(CO) 2 [P(OMe) 3 ] 2 (H)(CCSiMe 3 ) ( 4b ). In a slow subsequent process, or with promotion by Al 2 O 3 in hexane, the vinylidene compound Fe(CO) 2 [P(OMe) 3 ] 2 CC(H)SiMe 3 is formed. 3b or 4b are hydrolyzed to Fe(CO) 2 [P(OMe) 3 ] 2 CCH 2 ( 5c ) in the presence of SiO 2 . The reaction of disilylacetylene with 1a‐d results in the formation of disilylvinylidene complexes Fe(CO) 2 L 2 CC(SiMe 3 ) 2 (L PMe 3 , 7a ; LPEt 3 , 7b ; L P i Pr 3 , 7c ). An intermediate acetylene derivative could be isolated for L PEt 3 ( 6a ) and spectroscopically detected for L P(OMe) 3 ( 6b ), but could not be traced for L P(O i Pr) 3 . Further studies were devoted to the reactions of silyl diynes (Me 3 SiC≡CR, R C≡CSiMe 3 , p ‐C 6 H 4 ‐C‐CSiMe 3 ) with 1a‐c . In all cases the acetylene compounds Fe(CO) 2 L 2 (Me 3 −SiC≡CR) [L PEt 3 , R C≡CSiMe 3 , 8a ; R p ‐C 6 H 4 ‐C≡CSiMe 3 , 9a ; L P(OMe) 3 R CSiMe 3 , 8b ; R p ‐C 6 H 4 ‐C≡CSiMe 3 , 9b ] were isolated, but only for 8b was an equilibrium process observed to form the corresponding vinylidene derivative Fe(CO) 2 [P(OMe) 3 ] 2 CC(SiMe 3 )C‐C‐SiMe 3 ( 10b ). 10b hydrolyzes upon chromatography on silica gel to give Fe(CO) 2 [P(OMe) 3 ] 2 CCH‐C≡CSiMe 3 ( 11b ): Finally, the reaction of p ‐diethynylbenzene with 1a‐c was explored. The acetylido hydrido species Fe(CO) 2 L 2 (H)C≡C‐ p ‐C 6 H 4 ‐C≡CH was isolated in the case of L PEt 3 ( 12a ) and spectroscopically detected for L P(OMe) 3 ( 12b ). 12b and 12a transform spontaneously and in the presence of Al 2 O 3 in hexane, respectively, to the vinylidene complexes Fe(CO) 2 L 2 CC(H)R [R C 6 H 4 ‐C≡CH, L PEt 3 , 13a ; L P(OMe) 3 , 13b ]. 6a , 7a , and 8a have been characterized by single‐crystal X‐ray diffraction studies.