Reactions of the Phosphinidene-Bridged Complexes [Fe₂(η⁵-C₅H₅)₂(μ-PR)(μ-CO)(CO)₂] (R = Cy, Ph, 2,4,6-C₆H₂^tBu₃) with Diazoalkanes. Formation and Rearrangements of Phosphadiazadiene-Bridged Derivatives

Abstract

The phosphinidene complexes [Fe 2 Cp 2 (μ-PR)(μ-CO)(CO) 2 ] (Cp = η 5 -C 5 H 5 ; R = Cy, Ph, Mes*; Mes*=2,4,6-C 6 H 2 t Bu 3 ) react readily with diazoalkanes N 2 CR 0 R 00 (R 0 = H, R 00 = H, CO 2 Et, SiMe 3 ; R 0 =R 00 =Ph) in dichloromethane solution at room temperature or below to give the corresponding P:P-bridged phosphadiazadiene derivatives [Fe 2 Cp 2 (μ-RPN 2 CR 0 R 00 )(μ-CO)(CO) 2 ] (2) with high yield. The diazomethane derivative (Fe-Fe=2.6198(6) A ˚) is protonated selectively with HBF 4 3 OEt 2 at the P-bound nitrogen atom to yield the aminophosphide derivative [Fe 2 Cp 2 (μ-CyPNHNCH 2 )-(μ-CO)(CO) 2 ](BF 4 ) (Fe-Fe = 2.6126(5) A ˚). Compounds 2 decompose upon heating in toluene solution at 363 K to give the dimer [Fe 2 Cp 2 (CO) 4 ] as the only organometallic product. The same result was obtained when irradiating with visible-UV light toluene solutions of the phenylphosphinidene-derived compounds. In contrast, relatively selective decarbonylations could be induced photochemically when R = Cy, Mes*. The reaction products, however, were strongly dependent on the nature of all substituents present in compounds 2. The diazomethane derivative yielded a mixture of the P:N-bound phosphadiazadiene complex [Fe 2 Cp 2 (μ-CyPN 2 CH 2 )(μ-CO) 2 ] (major) and the phosphaalkene derivative [Fe 2 Cp 2 (μ-CyPCH 2 )(μ-CO)(CO)] (minor). In contrast, the ethyldiazoacetate derivative gave the paramagnetic complex [Fe 2 Cp 2 {μ-CyPN 2 CH(CO 2 Et)}(μ-CO)(CO)], possibly containing a μ-P:P,C-phosphadiazadiene ligand, which upon chromatography fully rearranges into the aminophosphide-iminoacyl complex [Fe 2 Cp 2 {μ-CyPNHNC(CO 2 Et)}(μ-CO)(CO)] (Fe-Fe = 2.6261(8) A ˚), possibly through a protonation/deprotonation sequence on the alumina surface. The trimethylsilyldiazomethane derivative instead gave directly the analogous aminophosphide-iminoacyl complex [Fe 2 Cp 2 {μ-CyPN(SiMe 3 )NCH}(μ-CO)(CO)], now resulting from an unusual 1,3-shift of the SiMe 3 group along the ligand backbone. Finally the photochemical treatment of the ethyldiazoacetate derivative of the supermesithylphosphinidene substrate gave the complex [Fe 2 Cp 2 {μ-Mes*PN 2 CH(CO 2 Et)}(μ-CO) 2 ] (Fe-Fe = 2.514(1) A ˚), containing a P:N-bridged phosphadiazadiene ligand bound to the dimetal center in a novel coordination mode, this involving the P-bound nitrogen atom, instead of the C-bound nitrogen. † Part of the Dietmar Seyferth Festschrift. This work is dedicated to Prof. Dietmar Seyferth, in recognition for his outstanding contribution to organometallic chemistry, both as an original researcher and as an efficient and kind editor of the prime specialized journal in the field.

P–N and N–Mo Bond Formation Processes in the Reactions of a Pyramidal Phosphinidene-Bridged Dimolybdenum Complex with Diazoalkanes and Organic Azides

“…As 10 Besides this, the NC lengths of ca. 1.29 Å in our dimolybdenum complexes are very close to the reference value of 1.27 Å for a N=C(sp 2 ) double bond, and the added proton/methyl is located at the P-bound N atom, which displays no significant pyramidalization, as found in the mentioned diiron complex.…”

“…In contrast, we observed no denitrogenation in the room-temperature reactions of pyramidal phosphinidene complexes (type C ) [Fe 2 Cp 2 (μ-PR)­(μ-CO)­(CO) 2 ] (R = Cy, Ph, Mes*) with benzyl azide and different diazoalkanes, which instead yielded isolable κ 1 P :κ 1 P -phosphatriazadiene- and κ 1 P :κ 1 P -phosphadiazadiene-bridged derivatives, respectively (Scheme ). − Subsequent denitrogenation could be induced thermally in the first case, to give the corresponding κ 1 P :κ 1 P -phosphaimine-bridged complex . Interestingly, reorganization of the diazoalkane derivatives could only be induced upon photochemical decarbonylation of the products first formed, which in most cases involved no denitrogenation but gave complexes with phosphadiazadiene ligands displaying novel P,C- and P,N-bound coordination modes, such as those shown in Scheme , among other unusual products …”

“… − Subsequent denitrogenation could be induced thermally in the first case, to give the corresponding κ 1 P :κ 1 P -phosphaimine-bridged complex . Interestingly, reorganization of the diazoalkane derivatives could only be induced upon photochemical decarbonylation of the products first formed, which in most cases involved no denitrogenation but gave complexes with phosphadiazadiene ligands displaying novel P,C- and P,N-bound coordination modes, such as those shown in Scheme , among other unusual products …”

DFT Mechanistic Insights into the Alkyne Insertion Reaction Affording Diiron μ-Vinyliminium Complexes and New Functionalization Pathways

“…The described mechanism is in accordance with the regiospecificity of the reaction and the stereochemistry exhibited by the products ( cis / trans and E / Z ), depending on the iminium substituents and the alkyne. These findings may have some general validity and might be extended to analogous alkyne insertion reactions occurring on dimetal frames. ,− Furthermore, we have described the synthesis of unprecedented organometallic motifs via vinyliminium C–H bond cleavage and subsequent C–C coupling with a variety of organic reactants, including the unusual activation of a cycloalkene. Vinyliminium complexes lacking of appropriate C–H function may be derivatized through one-electron reduction, the resulting radical species incorporating the [SPh] fragment in different ways according to the iminium substituents.…”

“…They can behave as η 2 terminal ligands or occupy bridging sites in polynuclear complexes, and this preliminary coordination may prelude to an impressive variety of reactions pathways . In particular, the intramolecular alkyne insertion into a metal–carbon bond, in di- and trinuclear metal complexes, represents an intriguing strategy to grow various hydrocarbyl fragments stabilized by bridging multisite coordination …”