Lithium and aluminium complexes supported by chelating phosphaguanidinates

Abstract

Diisopropylcarbodiimide, (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr, inserts into the lithium-phosphorus bond of in situ prepared "Ph(2)PLi(THF)(n)" to afford the lithium salt, [Li(Ph(2)PC{N(i)Pr}(2))(THF)(n)](x)(2a); alternatively, this compound can be made by deprotonation of the neutral phosphaguanidine, Ph(2)PC{N(i)Pr}{NH(i)Pr}(1a) with (n)BuLi. Displacement of the THF solvate in 2a is readily achieved with TMEDA to afford Li(Ph(2)PC{N(i)Pr}(2))(TMEDA)(3a). X-Ray crystallographic analyses show that 2a exists as a dimer in the solid state with a folded ladder structure and an N,N' chelating phosphaguanidinate, while 3a is monomeric with N,P-coordination of the ligand to lithium. Compound 2a reacts via a transmetallation pathway with AlMe(2)Cl to afford the dimethylaluminium complex, Al(Ph(2)PC{N(i)Pr}(2))Me(2)(4a), which can also be prepared by protonation of a methyl group of AlMe(3) using 1a. The formation of a series of dialkylaluminium compounds has been investigated employing this latter pathway using both 1a and the N,N'-dicyclohexyl analogue, Ph(2)PC{NCy}{NHCy}(1b), affording Al(Ph(2)PC{NR}(2))Et(2)(5a,b), Al(Ph(2)PC{NR}(2))(i)Bu(2)(6a,b) and the diphenylaluminium compound Al(Ph(2)PC{N(i)Pr}(2))Ph(2)(7a). The oily nature of most of the dialkyl compounds and high sensitivity to oxygen and moisture lead to difficulty in manipulation and characterization; however, NMR spectroscopy indicated highly pure products (>95%) upon removal of the solvent. The molecular structures of the crystalline examples 4a and 7a are reported, showing monomeric aluminium species with symmetrically chelating phosphaguanidinate ligands. The series of aluminium compounds AlLCl(2){L=[EC{NiPr}(2)](-): A, E=Me; B, E=Me(2)N; C, E=(Me(3)Si)(2)N and D, E=Ph(2)P} were investigated using density functional theory. In the more simple cases A and B, the delocalized electron density of the metallacycle was represented by a combination of the HOMO and an orbital of lower energy (A, HOMO-5; B, HOMO-6). The HOMO-1 in B was pi-bonded across the Me(2)N-C bond suggesting delocalization of electron density into the metallacycle. In the more complex systems C and D, delocalization within the metallacycle was less extensive due to the (Me(3)Si)(2)N- and Ph(2)P-moieties. A number of occupied orbitals in D, however, display phosphorus 'lone-pair' characteristics, indicating that these species have the potential to behave as Lewis bases in the formation of poly(metallic) systems.

Catalytic bond forming reactions promoted by amidinate, guanidinate and phosphaguanidinate compounds of magnesium

“…The 31 P{ 1 H} NMR of diphenylphosphaguanidinate derivative 6 shows a singlet at δ p −23.6, consistent with this ligand in the N,N'-chelated bonding mode (δ p range: −17.3 to −23.8). [38][39][40][42][43][44][45][46][47] Similarly, the chemical shift for the Cy 2 P-derivative, 8 (δ p −9.9) is consistent with other N,N'-chelated ligands incorporating this substitution at phosphorus (δ p range: −7.4 to −11.0). 44 Metathesis reactions of the Mg(N∩N)X(L) n compounds has been successfully performed using MOAr (M = Li, K; Ar = 2,6-t Bu 2 C 6 H 3 , 2,6-t Bu 2 -4-MeC 6 H 2 ) and MN{SiMe 3 } 2 (M = Li, K) to access aryloxide (11 and 12) and bis(trimethylsilyl)amide derivatives 13-15 (Scheme 4).…”

Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures

“…6). The predicted vertical excitations corresponding to the lowest energy absorption bands for 2-Cl, [3 + ], and [4 + ], with reasonably large oscillator strengths, were ligand-to-metal charge transfer (LMCT) transitions 6,[20][21][22]30,[34][35][36]54,[66][67][68][69] from guanidinate p orbitals 70,71 to cerium 4f orbitals in each case. For example, the major orbital contributions of the vertical excitation at 1.63 eV for [4 + ] were illustrated by TD-DFT calculations as HOMOÀ2 / LUMO+4 (13%), HOMO / LUMO (19%), and HOMO / LUMO+6 (48%).…”

Synthesis of Aminophosphines and Their Applications in Catalysis

“…In the initial experiments, complex 95 reacted with a solution of LiPPh 2 in THF purchased from Sigma-Aldrich. Reactions of the dimeric cyclopalladated complex 95 in THF with LiPPh 2 synthe- sized in our lab from either PPh 3 [72][73][74], or ClPPh 2 [75][76][77] or HPPh 2 [78,79] led to the formation of either μ-Cl-μ-PPh 2 complex 97 using 1 equiv. No traces of the desired aminophosphine 90 were formed.…”