Chirale Tripodliganden mit Phosphor‐ und Schwefeldonoren. Synthese und Komplexchemie

Chiral Tripod Ligands with Phosphorus and Sulfur Donors. Synthesis and Complex Chemistry Neopentane based tripod ligands CH 3 C(CH 2 X)(CH 2 Y)‐(CH 2 Z) with mixed donor groups X,Y,Z (PR 2 , SR, SH) are accessible via two different strategies. The functionalized thietane CH 3 (CH 2 X)ČH 2 SCH 2 allows stepwise introduction of P or S donors by substitution of the mesylate function and subsequent nucleophilic cleavage of the thietane ring. Tripod ligands 5 [CH 3 C(CH 2 X)(CH 2 Y)(CH 2 Z)] with up to three different donor groups (X = SH; Y = PPh 2 ; Z = P(4‐Tol) 2 , SCH 2 Ph, PPh 2 ) are thus available. As an alternative the neopentane derivatives 8 [CH 3 C(CH 2 X)(CH 2 Y)(CH 2 Cl)] which are easily assessible from CH 3 C(CH 2 OSO 2 Me)(CH 2 Br)‐(CH 2 Cl) ( 7 ) by stepwise substitution with phosphides LiPAr 2 (Ar = aryl) may be transformed to 9 [CH 3 C(CH 2 X)(CH 2 Y)(CH 2 SBzl)]. Under controlled conditions the S—benzyl bond of 9 is cleaved reductively without concomitant cleavage of P—Ar bonds. Ligand 5a [CH 3 C(CH 2 PPh 2 ) 2 (CH 2 SH)] reacts with Ni(BF 4 ) 2 · 6 H 2 O to yield the dinuclear species [(CH 3 C(CH 2 PPh 2 ) 2 ‐(CH 2 S)Ni) 2 ] 2+ ( 10 ). The two ligands are bonded in an equivalent way with each of the two nickel centers interacting with one of the two phosphane functions of the ligand; the thiolate functions form μ 2 ‐SR bridges between the two nickel atoms. The SCH 2 group at the four‐membered S 2 Ni 2 ring are in mutual cis position with the four‐membered ring bent along the sulfur–sulfur axis by 70°. The internal strain in 10 is analyzed by comparing its structure with the ones of [(CH 3 C(CH 2 ‐PPh 2 ) 3 NiSPh) 2 ] 2+ ( 11 ) and [(CH 3 C(CH 2 OH)(CH 2 PPh 2 ) 2 ‐NiOH) 2 ] 2+ ( 12 ).