Potassium and Yttrium Complexes of a Rigid Bis‐Phosphido POP‐Donor Ligand

Dilithiation of 4,5‐dibromo‐2,7‐di‐ tert ‐butyl‐9,9‐dimethyl‐xanthene (XBr 2 ) followed by addition of 2 equiv. of (2,4,6‐triisopropylphenyl)dichlorophosphine (TrippPCl 2 ) afforded 4,5‐bis[(2,4,6‐triisopropylphenyl)chlorophosphino]‐2,7‐di‐ tert ‐butyl‐9,9‐dimethylxanthene (XP 2 Cl 2 ), which was reduced to 4,5‐bis[(2,4,6‐triisopropylphenyl)phosphino]‐2,7‐di‐ tert ‐butyl‐9,9‐dimethylxanthene (H 2 XP 2 ) using excess LiAlH 4 . Deprotonation of H 2 XP 2 with excess KH in DME provided the dipotassium salt, [K 2 (XP 2 )(dme) n ] ( 1 ; n = 2.5–4), and stirring 1 in THF followed by recrystallization from hexanes yielded tetrametallic [K 4 (XP 2 ) 2 (THF) 4 ] ( 2 ) which features a central K 4 P 4 cage. Reaction of [YI 3 (THF) 3.5 ] with [K 2 XP 2 (dme) 2.5 ] afforded a mixture of products including [(XP 2 )YI(THF) 2 ] ( 3 ) and (PTripp) 3 ; pure 3 could be isolated in low yield by extraction with a minimum volume of hexanes or O(SiMe 3 ) 2 . In the solid state, 3 adopts a face‐capped trigonal bipyramidal coordination geometry with a planar xanthene backbone and an angle of 85° between the P(1)/C(4)/C(5)/P(2) and P(1)/Y/P(2) planes.