New Alkali Metal Boratabenzenes: Structures of K([18]‐Crown‐6)(C 5 H 5 BMe), of the Tetrahydropyran Solvate K(3,5‐Me 2 C 5 H 3 B−NMe 2 )(THP) 2 , and of Two THF Solvates of K[3,5‐Me 2 C 5 H 3 B−N(SiMe 3 ) 2 ]

The potassium salt K(C 5 H 5 BMe) ( 8 ) can be obtained from 2‐(Me 3 Sn)C 5 H 5 BMe ( 7 )/KO t Bu in toluene in essentially quantitative yield. Metalation of 1‐(dimethylamino)‐3‐methylene‐1,2,3,6‐tetrahydroborinine ( 9 ) with MN(SiMe 3 ) 2 (M = Na, K) in toluene afforded the unsolvated salts M(3,5‐Me 2 C 5 H 3 B−NMe 2 ) (M = Na: 11 ; M = K: 12 ). Morpholino derivatives M(3,5‐Me 2 C 5 H 3 B−NC 4 H 8 O) (M = Li: 17 ; M = Na: 18 ) and the potassium salt K[3,5‐Me 2 C 5 H 3 B−N(SiMe 3 ) 2 ] ( 19 ) were obtained similarly. The unsolvated salts are highly air‐ and water‐sensitive, colorless powders. Crystallization with the help of auxiliary Lewis bases provided crystalline solvates K([18]‐crown‐6)(C 5 H 5 BMe) ( 20 ), K(THP) 2 (3,5‐Me 2 C 5 H 3 B−NMe 2 ) ( 21 ), and the concomitant pseudopolymorphs K[3,5‐Me 2 C 5 H 3 B−N(SiMe 3 ) 2 ](THF) 4/3 (α ‐22 ) and K[3,5‐Me 2 C 5 H 3 B−N(SiMe 3 ) 2 ](THF) 3/2 (β ‐22 ), which were characterized structurally. The structures of α ‐22 (space group C 2/ c ) and β ‐22 (space group 6 1 22) display novel chain forms, which have no precedents in boratabenzene and cyclopentadienide chemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)