Insertion Reaction of Ketene into the Metal−Sulfur Bond:  Synthesis and Characterization of [Cp₂Ln(μ-η¹:η²-OC(SEt)CPh₂)]₂(Ln = Yb, Er, Sm, Y) and [Cp₂Er(μ-η¹:η²-OC(SEt)CPhEt)]₂

Treatment of [Cp 2 Ln(μ-SEt)] 2 with PhRC C O gives dimeric complexes [Cp 2 Ln(μ-η 1:η 2 -OC(SEt) CPhR)] 2 [R = Ph, Ln = Yb ( 1 ), Er ( 2 ), Sm ( 3 ), Y ( 4 ); R = Et, Ln = Er ( 5 )], which represent the first example of ketene insertion into a metal−sulfur bond and provide an efficient method for the synthesis of organolanthanides with a β -thiolate-substituted enolate ligand. It is found that an excess of ketene does not affect the nature of the final complexes, with only a single insertion being observed. All these complexes are characterized by elemental analysis and spectroscopic properties. The structures of complexes 1 ·C 6 H 5 CH 3, 2 ·C 6 H 5 CH 3, and 5 ·THF are determined through single-crystal X-ray diffraction analysis.