ABSTRACT
We report on the synthesis of an authentic SnâB-moiety realized in a stannaborenyl anion and stannaborenium cation. Starting with an oxidative addition of boron tribromide to a stannylene-phosphine Lewis pair [o-C6H4(Ar*BrSn-BBr2-PPh2)] (2a) [Ar* = C6H3(2,6-Trip)2, Trip = 2,4,6-C6H2iPr3] was synthesized. Reduction of 2a with magnesium yields the Grignard-type stannaborene [o-C6H4(Ar*SnâB{PPh2}MgBr{thf})]2 (3)2 featuring a SnâB double bond and a B-Mg interaction. Following an alternative protocol, hydride substitution at 2a yields the tinhydride [o-C6H4(Ar*HSn-BBr2-PPh2)] (4a). HBr elimination of 4a in reaction with MeNHC (MeNHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gives the carbene and phosphine stabilized stannyl-borylene [o-C6H4(Ar*BrSn-B{PPh2}{MeNHC})] (5) after simultaneous bromide transfer from boron to tin. In reaction of 5 with Li[Al(OC{CF3}3)4] or Na[BArF4] in a mixture of o-DFB/benzene a stannaborene [o-C6H4(Ar*SnâB{PPh2}{MeNHC})]+ [6] stabilized by the respective weakly coordinating anion was isolated (ArF = C6H3-3,5-(CF3)2, o-DFB = o-difluorobenzene). The phosphine and NHC-supported stannaborenium cation 6 adds ammonia at room temperature under splitting of a N-H bond and formation of Sn-NH2 and B-H bonds to give [o-C6H4(Ar*{H2N}Sn-BH{PPh2}{MeNHC})]+ (7).
ABSTRACT
A facile synthesis for unprecedented stibastannene (10) featuring a Sn=Sb-double bond together with the homologous arsa- (9) and phosphastannenes (8) is presented. Chloride abstraction from respective stannyl pnictinidenes [E=P (5), As (6), Sb (7)], which were made accessible by reduction of ECl3 addition products at an intramolecular phosphine-stabilized stannylene, gave the pnictastannenes in moderate yields. The pnictastannenes coordinate Pd(PPh3 )2 fragments (12-14) and the phosphastannene forms also a nickel coordination compound with the Ni(PPh3 )2 -fragment (11). 2,3-Dimethylbutadiene shows a [2+4]-cycloaddition (15-17) in reaction with the pnictastannenes (8-10). Products of a [2+2]-addition (18, 19) were isolated as the phosphaalkyne reaction products for 8 and 9. Addition of an O-H bond at the Sn=P-bond was found in reaction of water with phosphastannene 8. Reaction with ammonia afforded the NH3 -adducts (21-23) at the tin atom for pnictastannenes 8-10. Only in the case of the arsastannene an azide reaction product featuring a three membered Sn-As-N-ring was obtained.
ABSTRACT
Phenylacetylene adds [Ar*GeH2 -SnAr'], [Ar*GeH2 -PbAr'] and [Ar'SnH2 -PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn-H-Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin-orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH2 Ar*] with the trityl salt [Ph3 C][Al(OC{CF3 })4 ] to yield a four membered ring cation.
