Thermodynamic/Kinetic Control in the Isomerization of the [{tBuNP(m-NtBu)} 2 ] 2 Ion Andrew D. Bond, [a] Emma L. Doyle, [a] Felipe GarcÌa, [a] Richard A. Kowenicki, [a] David Moncrieff,* [b] Mary McPartlin, [c] LucÌa Riera, [a] Anthony D. Woods, [a] and Dominic S. Wright* [a] Introduction In recent years there has been considerable interest in anionic ligand arrangements containing Group 15/nitrogen frameworks. [1] The most exten- sively studied class of these spe- cies are the dianions [{RNE(m- NR)} 2 ] 2 (E = P, [2] As, Sb, Bi [1a] ), which have been shown to coor- dinate a broad range of metal ions with retention of their di- meric E 2 N 2 units. [1] For the phosphorus homologues, how- ever, dimerization of [(RN) 2 P]  monoanions into [{RNP(m- NR)} 2 ] 2 dianions can depend on the steric demands of the or- ganic substituents (R) (Scheme 1). Thus, the complex [{[tBuNP(m-NtBu)] 2 } 2 ]Li 4 (1) (Scheme 2a) contains [{tBuNP(m-NtBu)} 2 ] 2 ions, [2b] whereas [{[R(Mes)N] 2 PLi} 2 ] (Mes = 2,4,6-Me 3 C 6 H 2 ;R = 1-adamantyl, tBu) contain [{R(Mes)N} 2 P]  ions (Scheme 2 b). [3] [a] Dr. A. D. Bond, Dr. E. L. Doyle, F. GarcÌa, R. A. Kowenicki, Dr. L. Riera, Dr. A. D. Woods, Dr. D. S. Wright Chemistry Department, University of Cambridge Lensfield Road, Cambridge CB2 1EW (UK) Fax: (+ 44) 1223-336362 E-mail: dsw1000@cus.cam.ac.uk. [b] Dr. D. Moncrieff School of Computational Science & Information Technology Florida State University, Tallahassee, FL 32306±4120 (USA) [c] Prof. M. McPartlin Department of Health and Human Sciences London Metropolitan University Holloway Road, London N7 8DB (UK) Keywords: density functional calculations ¥ lithium ¥ phosphazane ¥ potassium ¥ sodium Abstract: The unique structure of [(tBuN) 2 PK] ¥ (2) (containing [(tBuN) 2 P]  mono- anions) is in stark contrast to the previously reported Li + analogue [{[tBuNP(m- NtBu)] 2 } 2 ]Li 4 (1) (containing the dimeric [{tBuNP(m-NtBu)} 2 ] 2 ion). DFT and 31 P NMR spectroscopic studies reveal that the formation of the monoanion ar- rangements are most thermodyamically favored for Li, Na, and K, 1 being the product of kinetic control and 2 being the product of thermodynamic control. Scheme 1. Notional equilibrium between the [{RNP(m-NR)} 2 ] 2 ion and [(RN) 2 P]  ions. Scheme 2. a) Structure of the ’double-cubane’ aggregate [{[tBuNP- (m-NtBu)] 2 } 2 ]Li 4 (1); b) Structure of [{[R(Mes)N] 2 PLi} 2 ] (Mes = 2,4,6- Me 3 C 6 H 2 ;R = 1-adamantyl, tBu). Chem. Eur. J. 2004, 10, 2271 ± 2276 DOI: 10.1002/chem.200305762 ¹ 2004 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim 2271 FULL PAPER