N-Geminal P/Al Lewis Pair–Alkyne Dipolar Cycloaddition to the Zwitterionic C₂PNAl-Heterocyclopentene

Abstract

The N-geminal P/Al Lewis pair [Ph 2 PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ] 2 ( 1 ) has been prepared and studied for reaction with a series of alkynes. The reaction of 1 with RC≡CR yielded zwitterionic C 2 PNAl-heterocyclopentene [Ph 2 ⌜ PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ](CR= ⌝ CR) (R = Me ( 2 ), Ph ( 3 )); with PhC≡CEt produced two isomers, [Ph 2 ⌜ PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ](CPh= ⌝ CEt) ( 4a ) and [Ph 2 ⌜ PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ](CEt= ⌝ CPh) ( 4b ); and with other alkynes generated [Ph 2 ⌜ PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ](CR 1 = ⌝ CR 2 ) (R 1 , R 2 = CO 2 Et, Ph ( 5 ); SiMe 3 , Ph ( 6 ); PPh 2 , Ph ( 7 ); SiMe 3 ,H ( 8 ); H, EtO ( 9 )). Natural bond orbital analysis of the charge separation of the C≡C bond of alkynes was carried out, and then, the electronic matching interaction mode between the combined Lewis acid (AlEt 2 ) and base (PPh 2 ) groups of 1 and the C≡C bond of such alkynes was discussed. Reactions of 1 with alkene, nitrile, and carbodiimide molecules were also carried out, and cycloaddition compounds 10 – 12 were produced.

Element‐Ligand Cooperativity with p‐Block Elements

“…Importantly, the terminal alkynes undergo 1,2‐addition, in contrast to the typically observed acid‐base reaction path . Such 1,2‐reactivity of alkynes was also found for geminal aluminum/phosphorus and gallium/phosphorus FLPs.…”

Reactivity of N-Phosphinoguanidines of the Formula (HNR)(Ph2PNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from N-Phosphinoguanidinates to Phosphinimine-Amidinates

“…The latter shifts are only about 10 ppm downfield from those of the other Al phosphinimine-amidinato complex previously reported, [Al-{κ 2 -N,N′-(N i Pr)C(N i Pr)(PPh 2 NDipp)}Et 2 ]. 5 The 1 H and 13 C{ 1 H} NMR spectra of 3a−c denote the presence of a symmetry plane, which is defined by the five-membered AlNCPN metallacycle, thus accounting for the same number of resonances as those found for compounds 2a−c in both spectra. The AlMe 2 fragment for compounds 3a−c originates slightly downfield singlet resonances in both spectra when compared to those in 2a−c in the range −0.01 to −0.07 ppm in the 1 H NMR spectra, and ca.…”

“…The potential interest in devising efficient synthetic procedures to prepare new κ 2 -N,N′-phosphinimine-amidinato complexes stems from (i) the paucity of examples found in the literature, the only ones being another Al complex of formula [Al{κ 2 -N,N′-(N i Pr)C(N i Pr)(PPh 2 NDipp)}Et 2 ] 5 and phosphinimineimidazolate derivatives of Na and Rh, 6 and (ii) the fact that conventional synthetic routes to these derivatives usually involve the use of hazardous chemicals, such as organic azides, and multistep processes. 6 As a follow-up to our previous communication, and to attest the scope of the aforementioned ligand rearrangement reaction for the synthesis of new phosphinimine-amidinato compounds, in this full paper we study the reactivity of three Nphosphinoguanidines (one of them reported for the first time, the cyclohexyl derivative (HNCy)(Ph 2 PNCy)C(NDipp) (1c)) toward the following four metal alkyls: the already mentioned AlMe 3 and ZnEt 2 as well as two s-block compounds, Mg n Bu 2 and n BuLi.…”

“…A mechanism for this unprecedented ligand rearrangement reaction was proposed, supported by DFT calculations, which involved a carbodiimide deinsertion reaction followed by a [3 + 2] cycloaddition (Scheme ). The potential interest in devising efficient synthetic procedures to prepare new κ 2 - N,N ′-phosphinimine-amidinato complexes stems from (i) the paucity of examples found in the literature, the only ones being another Al complex of formula [Al­{κ 2 - N,N ′-(N i Pr)­C­(N i Pr)­(PPh 2 NDipp)}­Et 2 ] and phosphinimine-imidazolate derivatives of Na and Rh, and (ii) the fact that conventional synthetic routes to these derivatives usually involve the use of hazardous chemicals, such as organic azides, and multistep processes …”

Bonding and Reactivity of Gallium and Aluminium Coordination Complexes

“…Complexes of the formula R2AlPR2, such as the landmark Trip2AlP(SiPh3)Ad (CXLI, Figure 103), 268 are relatively uncommon 269 and almost all have not had any significant reactivity studies published on them. Recently the reactivity of aluminium phosphine complexes has been centred around their use as FLPs, with bridged R2P-X-AlR2 (X = C,N) complexes such as CXLII being used to activate alkynes, 270 alkenes, 271 isocyanates, [271][272][273] CO2, [271][272][273][274] and H2. 247…”