Metal Centered Cleavage of E≡E Bonds (E = Si, Ge): The Mononuclear Rhodium Bis(Tetrylidyne) Complexes [Rh(≡ER) 2 (PMe 3 ) 2 ] +

Mononuclear bis(carbyne) complexes featuring two multiply bonded carbyne ligands at a single metal center, are an exceptionally rare class of organometallic compounds. Despite considerable advances in multiple bonding involving heavier group 14 elements, the synthesis of their heavier congeners, bis(tetrylidyne) complexes [L n M(ER) 2 ] (E = Si–Pb), remains extremely challenging owing to the lack of suitable synthetic strategies. Herein we report experimental and theoretical studies of the Rhodium bis(tetrylidyne) complex salts [Rh(ETbb) 2 (PMe 3 ) 2 ][B(Ar F ) 4 ] ( [2-E][B(Ar F ) 4 ] ; E = Si, Ge; Tbb = C 6 H 2 -4- t Bu-2,6-(CH(SiMe 3 ) 2 ) 2 ; Ar F = C 6 H 3 -3,5-(CF 3 ) 2 ). The complexes [2-E][B(Ar F ) 4 ] were obtained by chloride abstraction of the tetrylidyne-chlorotetrylidene complexes [Rh(ETbb)(EClTbb)(PMe 3 ) 2 ] ( 1-E ) with Na[B(Ar F ) 4 ]. Complexes 1-E were prepared by a E≡E triple bond cleavage reaction of the ditetrylynes E 2 (Tbb) 2 with [RhCl(PMe 3 ) 2 ] 2 . The molecular structures of [2-E] + feature two almost linearly coordinated tetrel centers, that are bonded to the Rh center via two very short Rh−E bonds (Rh−Si1 = 2.1310(7) Å, Rh−Si2 = 2.1240(7) Å; Rh−Ge1 = 2.2093(2) Å, Rh−Ge2 = 2.1976(2) Å). The electronic structure calculations in combination with the assessment of the thermochemical properties corroborate the presence of two highly polar Rh≡E triple bonds in [2-E][B(Ar F ) 4 ] . Cyclic voltammetric studies show a reversible electrochemical oxidation and reduction of the cations [2-E] + . The electrophilic character of the tetrel center is reflected in the reactions of [2-E][B(Ar F ) 4 ] ] with LiMe yielding the tetrylidyne-methyltetrylidene complexes [Rh(ETbb)(EMeTbb)(PMe 3 ) 2 ] ( 5-E ).