BORYLCYCLOPENTADIENIDES

The cyclopentadienylboranes C(5)H(5)BR(2) 1-4 (R = NMe(2), 1/2(OCMe(2) )(2), Pr-i, Me) are synthesized from alkali metal cyclopentadienides M Cp (M = Li, Na) and BCl(NMe(2))(2), ClB (OCMe(2))(2), BClPr2i, and BBr Me(2), respectively. Compound 1 reacts with lithium dialkylamides (LiN Me(2), LDA, LiTMP) in THF or with elemental sodium to give the salts M [C5H5B(NMe(2))(2)] [M(5) with M = Li, Na]. Compounds 2 and 3 are metal ated by LiTMP, and compounds 3 and 4 by cyclopentadienides MCp (M = Li , Na) to give borylcyclopentadienides or boratafulvenes M[C(5)H(5)BR(2 )] M(6)-M(8) (R = 1/2(OCMe(2))(2), Pr-i, Me). Estimated (NMR) room tem perature equilibrium constants for the systems 1-4/LiCp in THF are 0.5 , 4, >300, and >300, respectively; they show that dialkylboryl substit uents stabilize cyclopentadienide ions markedly. The triclinic THF sol vate Na(THF)(5) (=10) forms an approximately trigonal helix with alter nating Na(THF)(+) and anion units, while the tetragonal tetrahydropyra n solvate Na(THP)(5) (=11) forms a tetragonal helix. The monoclinic so lvate Li(12-crown-4)-(6) (=12) is molecular, and the orthorhombic Na(T HP)(2)(8) (=13) displays a chain structure. The B-C1 distances [154.5( 2) for 11, 148.8(8) for 12, and 150.8(4) pm for 13], lengthened C1-C2/ C1-C5 distances (av) (142.5 for 11, 142.1 for 12, and 143.6 pm for 13) , slightly lengthened C3-C4 distances (140.0 for 11, 141.1 for 12, and 143.5 pm for 13), and shortened C2-C3/C4-C5 distances (av) (140.3 for 11, 137.3 for 12, and 137.9 pm for 13) are caused by pi interactions (11 < 12, 13) between the C-5 ring and the boryl function. These inter actions are weak in the case of the B(NMe(2))(2) group and quite marke d for the B(OCMe(2))(2) and BMe(2) groups.