First Brønsted Acid-Induced Ring Expansion of an Oxaphosphirane Complex: A Combined Experimental and DFT Study

Abstract

a R denotes ubiquitous organic substituents; E denotes O or NR; [M] denotes a W(CO) 5 group. MWB(W) level. Crystallographic data of 6a and 7a have been deposited at the Cambridge Crystallographic Data Centre under the numbers CCDC-671013 (6a) and CCDC-701394 (7a). This data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

An Approach to 1,3,4‐Dioxaphospholane Complexes through an Acid‐Induced Ring Expansion of an Oxaphosphirane Complex: The Problem of Construction and Deconstruction of O,P‐Heterocycles

“…2 This recently changed with the advent of a facile and broadly applicable synthetic protocol based on Li/Cl phosphinidenoid complexes and their in situ reactions with carbonyl derivatives 3. 4 The first studies on ring‐expansion reactions of oxaphosphirane complexes by using strong Brønsted acids such as trifluoromethanesulfonic acid (TfOH) in the presence of nitriles enabled a P,O‐bond‐selective ring enlargement and thus access to 4,5‐dihydro‐1,3,4‐oxazaphosphole complexes;5 because of its ease, reliability, selectivity, and high yields, the protocol fulfills crucial criteria of click reactions 6. A surprising and ambiguous reactivity came to the fore if nitriles were not present7 and/or fluoroboronic acid8 was used.…”

“…Compared to the acid‐induced ring expansion of 9 with nitriles,5 three important differences deserve special mention: 1) The formation of the intermediate [ 11 ][OTf] is less favored than the formation of the Ritter‐type adduct from the reaction of [ 9 ][OTf] with acetonitrile. This is in agreement with the weaker nucleophilicity of acetaldehyde compared to acetonitrile.…”

Synthesis and Reactivity of an Unusual Ferrocenophane Bis(carbene complex)

“…[5] More recently, we developed new synthetic methodologies based on 2H-azaphosphirene complexes that provide facile access to four- [6] and five-membered [7,8] heterocycles under mild oxidative [7] or protic [8] conditions, thus introducing the "clickchemistry" concept to the field of phosphorus heterocyclic chemistry. We demonstrated that this new synthetic concept can be easily extended to oxaphosphirane [9] and azaphosphiridine [10] complex chemistry. In addition, di-and polymetallic transition metal complexes have attracted considerable interest in recent years.…”

Protonation‐Induced Rearrangement of an Oxaphosphirane Complex

“…The first designed application was found in the triflic acid induced PÀO ring expansion reaction with nitriles. [22] We accidentally discovered a thermal C À O bond cleavage reaction that provides access to novel O,P,C cage ligands. [23] As the titanium(III)-induced ring-opening of oxiranes has found numerous synthetic applications, [24] the feasibility of C À O and/or P À O bond cleavage of an oxaphosphirane complex by titanium(III) has also recently been investigated theoretically.…”