posted on 2019-07-10, 19:14authored byNiklas Aders, Lukas Keweloh, Damian Pleschka, Alexander Hepp, Marcus Layh, Friedhelm Rogel, Werner Uhl
The P–H functionalized
FLPs R(H)PC(AlBis2)C(H)-CMe3 (1a, R = Bis; 1b, R = Mes; Bis
= CH(SiMe3)2) combine the typical FLP properties
based on Lewis acidic Al and basic P atoms with the reactivity of
a P–H bond. They allow the coordination of substrates followed
by hydrophosphination with the activated P–H group. Reactions
of 1a with R′–NCS (R′
= Ph, CMe3) or of both FLPs with Et–NCCPh2 afforded five-membered AlCPCS/N heterocycles (4 and 5) via coordination of CS or CN
bonds to the FLP backbone. Isomerization by a 1,3-H shift from P to
N or C (6 and 7) was only achieved in the
presence of an auxiliary base (DABCO; 1–5 mol %). (Z)-1a coordinated CO2 to yield the
adduct 8, which features a five-membered AlCPCO heterocycle
with an exocyclic CO bond. Addition of bases such as DABCO
and DBU afforded by deprotonation of the P atom the compounds [Bis-PC(AlBis2)C(H)–CMe3(CO2)]−[HB]+ (9a, B = DABCO; 9b, B = DBU) that displayed hydrogen bonding between the ammonium
ions and the exocyclic O atom of the FLP adducts in solution and the
solid state. The stronger base n-BuLi afforded the
dimeric Li compound 10, in which the Li cation was coordinated
in a chelating manner to the oxygen atoms of one FLP adduct and additionally
to the exocyclic O atom of the second adduct, resulting in a four-membered
Li2O2 heterocycle. The related reaction of (Z)-1a with DABCO(SO2)2 led in contrast to the elimination of BisH and formation of a SO2-bridged dimer that features a central (AlOSO)2 heterocycle with Al–O and S–O single bonds. The resulting
unusual structural motifs may be derived from those of dialkylcarbamic
or dialkylamidosulfinic acids with the N atoms replaced by P atoms.