Synthetic and structural studies on some bis(cyclopentadienyl)molybdenum and -tungsten complexes containing doubly bonded tin or phosphorus

Nucleophilic Phosphinidene Complexes: Access and Applicability

“…The first stable 18-electron phosphinidene complexes were synthesized by Lappert and co-workers, [12] who treated lithium metallocene hydride [{Cp 2 MHLi} 4 ] with dichlorophosphine RPCl 2 (R = Mes*, (Me 3 Si) 2 CH) to obtain [Cp 2 M= PR] (1 a,b, M = Mo, W, respectively) as stable, red crystalline materials (Scheme 2). [12] The low-field 31 P NMR spectroscopy chemical shifts (R = Mes*; Mo (1 a) d = 799.5 ppm, W (1 b) d = 661.1 ppm) proved to be characteristic for terminal phosphinidene complexes.…”

“…[7][8][9][10] These advances were enabled by the discovery in the 1980s of the transient electrophilic species [(OC) 5 W = P À Ph] by the group of Mathey [11] and of the isolable nucleophilic phosphinidene complex [Cp 2 W=PÀMes*] by Lappert and co-workers (Cp = C 5 H 5 , Mes* = 2,4,6-tBuC 6 H 2 ). [12] Illustrative of the ensuing rapid progress in this field are two reviews by Cowley, one published in 1988, entitled "The Quest for Terminal Phosphinidene Complexes" [13a] and the other in 1997 "Terminal Phosphinidene and Heavier Congeneric Complexes. The Quest is Over".…”

Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

“…[1,2] However, although such complexes were first reported three decades ago, [3] they remain ar elatively rare class of metal-ligand multiple bond. This relative paucity reflects the inherent nature of the phosphinidene functional group,which as af ree moiety is very reactive due to the P-triplet ground state and unsaturated valence shell.[4] Stabilization of aphosphinidene by metal-coordination is an attractive strategy, [1] but normally also demands as terically bulky group at phosphorus to kinetically stabilize the M=PR linkage.Indeed, it is notable that under ambient conditions all isolable transition-metal phosphinidene complexes exhibit sterically demanding Rg roups to kinetically protect these vulnerable M=PR bonds; [3,[5][6][7][8][9] in abroader sense the only exceptions are where fundamental, elegant species such as H 2 M = PH (M = Ti,Z r, and Hf) have been prepared and spectroscopically observed under cryogenic conditions.[10] Early transitionmetal phosphinidene complexes are perhaps the most developed of all metal-phosphinidenes,s oi ti ss urprising that an early transition-metal parent phosphinidene has not yet been realized under ambient conditions.Recently,a spart of our work on actinide-ligand multiple bonds, [11] we reported uranium and thorium phosphinidene complexes using the parent phosphinidene (HP) 2À , [12] despite the large triplet-singlet energy gap of approximately 22 kcal mol À1 for free PH, [4g] which had previously only been seldom observed as af leeting spectroscopic intermediate or probed theoretically.[4] Those two actinide complexes are the only two M = PH complexes yet isolated outside cryogenic spectroscopic experiments,a nd were supported by the very sterically demanding triamidoamine ligand N(CH 2 CH 2 NSiPr …”

“…[1,2] However, although such complexes were first reported three decades ago, [3] they remain ar elatively rare class of metal-ligand multiple bond. This relative paucity reflects the inherent nature of the phosphinidene functional group,which as af ree moiety is very reactive due to the P-triplet ground state and unsaturated valence shell.…”

“…Indeed, it is notable that under ambient conditions all isolable transition-metal phosphinidene complexes exhibit sterically demanding Rg roups to kinetically protect these vulnerable M=PR bonds; [3,[5][6][7][8][9] in abroader sense the only exceptions are where fundamental, elegant species such as H 2 M = PH (M = Ti,Z r, and Hf) have been prepared and spectroscopically observed under cryogenic conditions. [10] Early transitionmetal phosphinidene complexes are perhaps the most developed of all metal-phosphinidenes,s oi ti ss urprising that an early transition-metal parent phosphinidene has not yet been realized under ambient conditions.…”