Unprecedented Ring–Ring Interconversion of N,P,C‐Cage Ligands

Abstract

The novel N,P,C-cage complexes 5 a-f and 6 a-f have been obtained by the reaction of the P-pentamethylcyclopentadienylphosphinidene complex 2, generated thermally from 2H-azaphosphirene complex 1, with N-methyl-C-arylcarbaldimines 3 a-f. Li/Cl phosphinidenoid complex 8 reacted with 3 a,b to give N,P,C-cage complexes 6 a,b, whereas with 3 c-f, complexes 6 c-f were obtained in negligible amounts only. Both types of ligand N,P,C-cage structures 5 and 6 were found to be in an unprecedented equilibrium, with 5 a,f as the predominant species. Transient electrophilic terminal phosphinidene complexes 10 a-f serve as intermediates in both ligand interconversions (5 a,f↔6 a,f), as evidenced through trapping reactions with phenylacetylene and N-methyl-C-phenylcarbaldimine, thus leading to the novel N,P,C-cage complexes 13 b and 15. DFT calculations predicted a small difference in the relative energies of the two types of N,P,C-cage ligands, and a remarkable stabilisation of the aminophosphinidene complex 10 as the common precursor, thereby providing an insight into this surprising 5-ring-3-ring interconversion. In depth analysis of intermediate 10 revealed the occurrence of both through-bond (conventional inductive/mesomeric effects) and through-space (non-covalent interactions) mechanisms, which amount to 67.8 and 14.4 kcal mol(-1), respectively, and account for the remarkable stabilisation of this intermediate.

Synthesis of the First Oxaphosphirane Iron Complexes

“…Since the first oxaphosphirane complex formation by formal cheletropic cycloaddition of a carbonyl component with a P 1 fragment coming from a in situ generated phosphinidene complex, an initial nucleophilic attack from O to the electrophilic phosphinidene P atom was assumed [11] . Only very recently, this was computationally proven [12] which was previously shown only for the reaction with imines [13] . However, the most recent and syntheticcally very useful “similar” reaction of Li/Cl phosphinidenoid complexes with carbonyl compounds has never been computationally explored, neither for the “classical” zerovalent group 6 pentacarbonyl complexes nor the herein reported reaction with tetracarbonyliron(0) fragments.…”

“…[11] Only very recently, this was computationally proven [12] which was previously shown only for the reaction with imines. [13] However, the most recent and syntheticcally very useful "similar" reaction of Li/Cl phosphinidenoid complexes with carbonyl compounds has never been computationally explored, neither for the "classical" zerovalent group 6 pentacarbonyl complexes nor the herein reported reaction with tetracarbonyliron(0) fragments. Therefore, the free energy surfaces of these reactions were inspected using acetaldehyde 7 as simple model carbonyl component and P-methyl substituted model Li/Cl phosphinidenoids bearing either W(CO) 5 8 a or Fe(CO) 4 8 b (Scheme 3).…”

“…Starting compound 1 was synthesized according to literature. All NMR spectra were recorded on a Bruker AVI-300 (300.1 MHz for 1 H; 282.4 MHz for 19 F; 75.5 MHz for 13 C, 59.6 MHz for and 121.5 MHz for 31 P) and Bruker AVI-400 (400.1 MHz for 1 H, 100.0 MHz for 13 C, and 162.1 MHz for 31 P) and Bruker AV III HD Prodegy 500 (500.2 MHz for 1 H, 125.8 MHz for 13 C and 202.5 MHz for 31 P) spectrometer at 298 K. The 1 H and 13 C NMR spectra were referenced to the residual proton resonances and the 13 C NMR signals of the deuterated solvents; 31 P were referenced to 85 % H 3 PO 4 and 19 F to CFCl 3 as external standards, respectively. Melting points were determined in one-side melted off capillaries using a Büchi Type S or a Carl Roth Type MPM-2 apparatus and are uncorrected.…”

Going for strain: synthesis of the first 3-imino-azaphosphiridine complexes and their conversion into oxaphosphirane complex valence isomers

“…Due to our longstanding interest in the chemistry of complexes possessing strained heterocyclic ligands having polar ring bonds such as 2H-azaphosphirenes, 7 oxaphosphiranes 8 and azaphosphiridines, 9 we contemplated about reactions of Li/Cl phosphinidenoid complexes 10 and cumulenes. The first example of this is reported herein, together with theoretical calculations of the ring strain energy of the hitherto unknown complexes VIII and a proposed pathway for their conversion into the first stable valence isomers of oxaphosphirane complexes.…”

Coordination of N2and Other Small Molecules to the Phosphorus Centre of RPW(CO)5: A Theoretical Study on the Janus Facets of the Stabilization/Activation Problem

“…The same holds for Löwdin bond orders (LBOs) (see the Supporting Information, Figure S1). Also the electron density ρ ( r ) at bond critical points (BCPs) has been frequently used as indicator for the interaction strength in organophosphorus chemistry, showing good correlation in this particular case with other descriptors (Figure b) and showing well‐defined separated tendencies for N‐ and C‐donor ligands. As a general trend, within the set of N‐donors the weakest P,N single bond interactions are those with sp 3 ‐hybridized ligands (amines), followed by sp 2 ‐ligands (imines and pyridine‐type N‐donor heterocycles) and sp‐ligands (N 2 , CN − , nitriles).…”