Unlocking Air- and Water-Stable Technetium Acetylides and Other Organometallic Complexes.

The first technetium complexes containing anionic alkynido ligands in an end-on coordination mode have been prepared by using the nonprotic, cationic precursor mer , trans -[Tc(SMe 2 )(CO) 3 (PPh 3 ) 2 ] + . This cation acts as a functional analogue of the highly reactive 16-electron metallo Lewis acid {Tc(CO) 3 (PPh 3 ) 2 } + in reactions with alkynes, acetylides, and other organometallic reagents. Such reactions give a variety of organometallic technetium complexes in excellent yields and enable the preparation of [Tc(CH 3 )(CO) 3 (PPh 3 ) 2 ], [Tc(Ph)(CO) 3 (PPh 3 ) 2 ], [Tc(Cp)(CO) 2 (PPh 3 )], [Tc(═CCH 2 CH 2 CH 2 O)(CO) 3 (PPh 3 ) 2 ] + , [Tc(═CCH 2 CH 2 CH 2 CH 2 O)(CO) 3 (PPh 3 ) 2 ] + , [Tc(C≡C-H)(CO) 3 (PPh 3 ) 2 ], [Tc(C≡C-Ph)(CO) 3 (PPh 3 ) 2 ], [Tc(C≡C- t Bu)(CO) 3 (PPh 3 ) 2 ], [Tc(C≡C- n Bu)(CO) 3 (PPh 3 ) 2 ], [Tc(C≡C-SiMe 3 )(CO) 3 (PPh 3 ) 2 ], and [Tc{C≡C-C 6 H 3 (CF 3 ) 2 }(CO) 3 (PPh 3 ) 2 ]. The bonding situation in the alkynyl complexes is compared to that in corresponding alkyl- and arylnitrile and -isonitrile complexes. [Tc(N≡C-Ph)(CO) 3 (PPh 3 ) 2 ](BF 4 ), [Tc(C≡N-Ph)(CO) 3 (PPh 3 ) 2 ](BF 4 ), [Tc(N≡C- t Bu)(CO) 3 (PPh 3 ) 2 ](BF 4 ), and [Tc(C≡N- t Bu)(CO) 3 (PPh 3 ) 2 ](BF 4 ) were prepared in high yields by ligand exchange reactions starting from mer , trans -[Tc(OH 2 )(CO) 3 (PPh 3 ) 2 ](BF 4 ). The novel complexes were characterized by single-crystal X-ray diffraction and spectroscopic methods. In particular, 99 Tc nuclear magnetic resonance spectroscopy proved to be an invaluable and sensitive tool for the characterization of the complexes. Density functional theory calculations strongly suggest similar bonding situations for the related alkynyl, nitrile, and isonitrile complexes of technetium.