The 2c-2e- P-P bonded dimers [(CH)2(NR)2P]2 dissociate in solution to give the persistent new 7pi radicals [(CH)2(NR)2P]*, which are isoelectronic with the well known S/N thiazolyl radicals.

The quantification of Lewis acidity is accomplished by a deuterated quinolizidine probe utilizing 2H NMR spectroscopy. The chemical shifts of the 2H NMR signals for aluminum, boron, titanium, and zinc halides are reported. The rate constants for Lewis acid catalyzed reactions were determined by utilizing UV/Vis spectroscopy for Diels–Alder and Povarov reactions under pseudo‐first‐order conditions. The magnitude of the 2H NMR chemical shifts correlates with the rate constants of the organic transformations for many Lewis acids investigated in the same order, whereas some deviations are identified.

Transition metal-mediated dehydrocoupling is a developing synthetic tool for the preparation of an extensive range of main group element-element bonded species, with broad applications to molecular and polymeric materials. Recent results have stressed the relationship between this class of transition metal reagents and their entirely main group counterparts. But what are the similarities and differences between transition metal and main group systems?

Reaction of the redox-active base Sn(NMe(2))(2)/(n)BuLi with o-phenylene diamine leads to oxidative dehydrocoupling and rearrangement into the triazolyl anion.

The room-temperature reactions of stannocene, Cp*(2)Sn, with a range of primary phosphines, RPH(2), result in diphosphanes [RP(H)P(H)R]. The reactions involving Cp*(2)SnCl(2), however, result in catalytic dehydrocoupling; the first example of main group metal catalysed dehydrocoupling to be identified.

We have previously developed a strategy for the preparation of heterometallic main-group imido (RN 2À ) and phosphinidene (RP 2À ) compounds involving stepwise deprotonation of REH 2 (E = N,P) with alkali-metal organometallics (for example nBuLi), followed by reaction with M(NMe 2 ) n (M = As, Sb, Bi, n = 3; Sn n = 2; Scheme 1).[1] Recently, however, we have recognized the behavior of this type of mixed-metal system as superbases. [2] This effect was first apparent in the reaction of MesPH 2 (Mes = 2,4,6-Me 3 C 6 H 2 ) with Sn(NMe 2 ) 2 /PhCH 2 Na, which gives the unusual stannate ion [Sn{P(2-CH 2 -4,6-Me 2 C 6 H 2 )}{PMes}] 3À [3] as a result of deprotonation of a PH 2 group and an ortho-CH 3 group. Remarkably, quadruple deprotonation of the PH 2 and NH 2 groups occurs in 1-NH 2 -2-PH 2 -C 6 H 4 (LH 4 ) using a similar Sn(NMe 2 ) 2 /nBuLi mixture, givingcontaining the L 4À tetraanion and LC 3À radical.[4]Herein we report the reaction of 1,2-(PH 2 ) 2 C 6 H 4 with Sb(NMe 2 ) 3 /nBuLi, which results in the complete deprotonation of the PH 2 groups, giving the 6p-aromatic anion [1,2-C 6 H 4 P 2 Sb] À . Upon one-electron reduction, the [1,2-C 6 H 4 P 2 Sb] 2 4À tetraanion is formed. As established from DFT calculations, this highly charged, Sb À Sb-bonded distibane is best described as a dimer of two 7p-[1,2-C 6 H 4 P 2 Sb]C 2À radicals (Scheme 2 a) and is valence-isoelectronic with the important class of sulfur/nitrogen-based thiazolyl radicals (Scheme 2 b).[5]Lithiation of 1,2-(PH 2 ) 2 C 6 H 4 (1 equiv) with nBuLi (2 equiv) in tmeda (tmeda = Me 2 NCH 2 CH 2 NMe 2 ) followed by reaction with Sb(NMe 2 ) 3 (0.67 equiv) gives [Li-(tmeda) 2 ]+ [1,2-C 6 H 4 P 2 Sb] À (1) after crystallization from THF/tmeda. However, black crystals of [{1,2-C 6 H 4 P 2 Sb} 2 {Li-(tmeda)} 4 ] (2) [6] are obtained if this reaction is undertaken in toluene and the product crystallized from toluene/tmeda. Compound 2 presumably arises from one-electron reduction of the 6p-aromatic anion of 1 (Scheme 3). The diamagnetic nature of 2 persists in the solid state and in dilute solutions in toluene as a result of spin-pairing of the electrons within the SbÀSb-bonded dimer, as shown by the structural characterization (see below). This situation contrasts with the behavior of valence-isoelectronic dithiazolyl dimers, for which a dissociation energy of about 0 kJ mol À1 results in extensive dissociation in solution.[5]

The room-temperature reactions of Sn(NMe(2))(2) with less sterically demanding primary phosphines (RPH(2)) give the homoleptic phosphanediide compounds [SnPR](n) in high yields (R=tBu (1a), cyclohexyl (1b), 1-adamantyl (1c)). However, the room-temperature reaction of Mes*PH(2) (Mes*=2,4,6-tBu(3)C(6)H(2)) with Sn(NMe(2))(2) gives the model intermediate [{SnPMes*}(2)(mu-NMe(2))SnP(H)Mes*] (3), together with the product of complete deprotonation [SnPMes*](3) (4). Phosphorus--phosphorus bonded products are produced in these reactions at elevated temperatures. If the reaction producing 1a is heated to reflux then [tBuP(H)P(H)tBu] is produced as the major product (together with tin metal). The novel octanuclear cage [{SnPtBu}(7)Sn(PtBu)(3)] (2) can also be isolated in low yield, resulting from formal addition of the heterocyclic stannylene [(tBuP)(3)Sn] to a Sn-P single bond of the intact structure of 1a. Prolonged heating of the reaction producing 3 and 4 leads to the formation of the diphosphene [PMes*](2) (5) and tin metal. The X-ray structures of the heptamer 1a (n=7), octanuclear 2 and trinuclear 3 are reported.

Dilithiation of 1,2-(PH2)2C6H4 with nBuLi followed by reaction with Sn(NMe2)2 in the presence of the Lewis base donor tmeda [Me2NCH2CH2NMe2] gives [(C6H4P2Sn)(Li.tmeda)2] , containing the phosphide-stabilised, 6pi stannylene dianion [C6H4P2Sn]2-.