Bis(diisopropylamino)phosphanyldiazomethane: A building block for the synthesis of stable carbene and nitrilimines

Abstract

RESULTS AND DISCUSSIONThe ability of transition metals to stabilize electron-deficient species such as carbenes, nitrenes, phosphinidenes [ 11, or other types of highly reactive organic or inorganic species is now well established. Less often, it has been shown that a similar role could be played by heavier main group elements. For example, sulfenylnitrenes [2] or phosphanylnitrenes [3] can be relatively stable. Here, we report that the [bis(diisopropylamino)-phosphanyl](trimethyIsilyl)carbene 2 is an isolable compound possessing the characteristics of a normal carbene and of a polarized A5-phosphaacetylene. We also show that the precursor of this compound, namely the [bis(diisopropylamino)phosphanyl](trimethylsilyl)diazomethane 1, is an excellent building block for the synthesis of the first stable nitrilimine 3.Diazo compounds are classical precursors of carbenes. Although diazo-A5-phosphorus derivatives are well documented [4], as far as we know, no examples of molecules possessing a diazo group bonded to a A3-phosphorus atom have been reported before our work [5,6]. This class of compounds, like phosphane azides, could have been very unstable due to possible intermolecular reactions of the diazo moiety with the phosphorus lone pair [7]. Taking into account the observed stability of the bis(diisopropy1amino)phosphane azide [3, 81 we chose to prepare the (trimethylsilyl)[bis(diisopropylamino)phosphanyl]diazomethane 1. 'Treatment of the lithium salt of (trimethylsily1)diazomethane [9] with a stoichiometric amount of bis(diisopropy1amino)chlorophosphane [ 101 led to the desired product 1 in 85% isolated yield (Scheme 1).

Stable Noncyclic Singlet Carbenes

“…In this respect, the possible participation of excited states of the phosphinocarbenes has been recognized, especially when forcing experimental conditions are used. 100 Carbenes Stabilized by an Amino Group. Because of their high-lying vacant orbital, diaminocarbenes III are not prone to undergo C-H insertion reactions.…”

“…[3 + 2]-Cycloaddition reactions across the PC bond of the phosphinosilylcarbene Ia have been observed with trimethylsilyl azide and nitrous oxide (Scheme ). The diazo compounds 68 and 69 were isolated in high yields, and the initially formed [3 + 2]-cycloadduct 67 was detected spectroscopically at 4 °C. ,, …”

“…A similar reaction was observed for the stable phosphinosilylcarbene Ia . Upon pyrolysis at 300 °C under vacuum, the five-membered heterocycle 74 was obtained in 90% yield as a mixture of four diastereomers. , The total and different regioselectivity observed in these C−H insertion reactions is surprising and may result from subtle stereoelectronic effects and/or alternative mechanistic pathways. In this respect, the possible participation of excited states of the phosphinocarbenes has been recognized, especially when forcing experimental conditions are used …”