Li/X Phosphinidenoid Pentacarbonylmetal Complexes: A Combined Experimental and Theoretical Study on Structures and Spectroscopic Properties

Abstract

The synthesis of P-F phosphane metal complexes [(CO)5M{RP(H)F}] 2a-c (R = CH(SiMe3)2; a: M = W; b: M = Mo; c: M = Cr) is described using AgBF4 for a Cl/F exchange in P-Cl precursor complexes [(CO)5M{RP(H)Cl}] 3a-c; thermal reaction of 2H-azaphosphirene metal complexes [(CO)5M{RP(C(Ph)═N}] 1a-c with [Et3NH]X led to complexes 3a-c, 4, and 5 (M = W; a-c: X = Cl; 4: X = Br; 5: X = I). Complexes 2a-c, 3a-c, 4, and 5 were deprotonated using lithium diisopropylamide in the presence of 12-crown-4 thus yielding Li/X phosphinidenoid metal complexes [Li(12-crown-4)(Et2O)n][(CO)5M(RPX)] 6a-c, 7a-c, 8, and 9 (6a-c: M = W, Mo, Cr; X = F; 7a-c: M = W, Mo, Cr; X = Cl; 8: M = W; X = Br; 9: M = W; X = I). This first comprehensive study on the synthesis of the title compounds reveals metal and halogen dependencies of NMR parameters as well as thermal stabilities of 6a, 7a, 8, and 9 in solution (F > Cl > Br > I). DOSY NMR experiments on the Li/F phosphinidenoid metal complexes (6a-c; M = W, Mo, Cr) rule out that the cation and anion fragments are part of a persistent molecular complex or tight ion pair (in solution). The X-ray structure of 6a reveals a salt-like structure of [Li(12-crown-4)Et2O][(CO)5W{P(CH(SiMe3)2)F}] with long P-F and P-W bond distances compared to 2a. Density functional theory (DFT) calculations provide additional insight into structures and energetics of cation-free halophosphanido chromium and tungsten complexes and four contact ion pairs of Li/X phosphinidenoid model complexes [Li(12-crown-4)][(CO)5M{P(R)X}] (A-D) that represent principal coordination modes. The significant increase of the compliance constant of the P-F bond in the anionic complex [(CO)5W{P(Me)F}] (10a) revealed that a formal lone pair at phosphorus weakens the P-F bond. This effect is further enhanced by coordination of lithium and/or the Li(12-crown-4) countercation (to 10a) as in type A-D complexes. DFT calculated phosphorus NMR chemical shifts allow for a consistent interpretation of NMR properties and provide a preliminary explanation for the "abnormal" NMR shift of P-Cl derivatives 7a-c. Furthermore, calculated compliance constants reveal the degree of P-F bond weakening in Li/F phosphinidenoid complexes, and it was found that a more negative phosphorus-fluorine coupling constant is associated with a larger relaxed force constant.

Synthesis and Ambiphilic Reactivity of Metalated Diorgano‐Phosphonite Boranes

“…The 31 PNMR signals of K[3b-d]s till show the splitting arising from spin coupling between the 31 Pa nd 11 B( I= 3/2) nuclei, but lack the doublet structure caused by 1 J PH couplinga cross a PÀHb ond, thus confirming that deprotonationw as successful. Comparison of the 31 Pa nd 11 BNMR data of K[3b-d]w ith those of precursors 2b-d (Table 1) showsthat the metalation induces am odest rise in d 11 Ba long with as tark increase of some 170 ppm in d 31 Pa nd ad ecrease in the magnitude of 1 J P11B .T he same trends hold for diaminophosphide boranes. [3] The increase in d 31 Pi sc ounter intuitive when compared to the negative metalation shifts of alkyl and aryl phosphineb oranes, [3] but prevails as well in phosphinidenoid complexes Li solv [(Me 3 Si) 2 CH-P(X){M(CO) 5 }] (X = halide,M= Cr,M o, W) featuring as ingle electronegative halide substituent on phospho- rus.…”

“…As imilar lengthening is also found in metalated aryl/alkyl-phosphide boranes [15] as well as M[1a]( M= Na,K ) [3b] and K[3b], butthe P-Bd istance in Li[5c]i sb eyond the previously knownr ange of 1.94 to 1.97 . [3b, 13, 15] This exceptional lengthening seems well suitable to explain both the easy displacemento ft he borane unit as well as the absence of significant line broadening or splitting arising from 31 P, 11 Bs pin coupling in the 31 PNMR spectrum.…”

Reactions of Li/Cl Phosphinidenoid Complexes with 1,3,4,5‐Tetramethylimidazol‐2‐ylidene: A New Route to N‐Heterocyclic Carbene Adducts of Terminal Phosphin­idene Complexes and an Unprecedented Transformation of an Oxaphosphirane Complex

“…Recently, we reported on the synthesis of P ‐Cl phosphinidenoid complexes having sterically demanding and hence weakly coordinating (organic) countercations such as 1,3‐di‐ tert ‐butylimidazolium,9 which also have stability up to ambient temperature. Cleavage of the tungsten–phosphorus bond was not observed, although theoretical results based on compliance constants3b had indicated a weak phosphorus–tungsten bond. Stimulated by this theoretical prediction a new study on the reactivity of Li/Cl phosphinidenoid complexes and a sterically less demanding N‐heterocyclic carbene (NHC), namely, 1,3,4,5‐tetramethylimidazol‐2‐ylidene (Me 2 IMe), was started.…”

“…In 1988 Yoshifuji et al introduced the term “phosphinidenoid”, proposing this low‐coordinate phosphorus compound as a reactive intermediate 2. Since the facile protocol for the generation of Li/Cl phosphinidenoid complexes at low temperature was reported in 2007,3a in‐depth studies on structure and bonding,3b as well as on applications, have been reported. One example to illustrate this is the field of oxaphosphirane complexes, which tremendously profited from the clean, high‐yield reaction of Li/Cl phosphinidenoid complexes with aldehydes and ketones 4.…”

Synthesis and Deprotonation of Aminophosphane Complexes: First K/N(H)R Phosphinidenoid Complexes and Access to a Complex with a P2N‐Ring Ligand

“…For example, the trityl Li/Cl phosphinidenoid complex (R=CPh 3 ) was found to be stable at ambient temperature for several hours . Despite detailed solution‐state NMR studies on a series of Li/X phosphinidenoid tungsten(0) complexes (X=F, Cl, Br, I), the isolation was difficult, and only one single‐crystal X‐ray structure has been reported so far . Within this series of Li/X phosphinidenoid complexes, only the reactivity of Li/Cl derivatives has been studied in greater detail, which has revealed mostly nucleophilic reactivity towards organic halides and the formal addition to π‐systems, such as alkynes, aldehydes, ketones, and imines, to give a wide variety of strained P‐heterocycles under mild conditions with a remarkable functional group tolerance.…”