Even and odd: uranium(IV) complexes with two,four, and six salicylaldiminate ligands with an unusual κ1-coordination mode

We report the synthesis and structural determination of three uranium(IV) complexes bearing two, four, and six salicylaldiminate ligands. Reaction of UI₄(1,4-dioxane)₂ with two, four, and six equivalents of K[OC₆H₄C(H)=N(2,6-ⁱPr₂C₆H₃)], 1, yielded [(2,6-ⁱPr₂C₆H₃)N=C(H)C₆H₄O-κ²(O,N)]₂UI₂(NCCH₃), 2, [(2,6-ⁱPr₂C₆H₃)N=C(H)C₆H₄O-κ¹(O)]₂[(2,6-ⁱPr₂C₆H₃)N=C(H)C₆H₄O-κ²(O,N)]₂U(THF), 3, and {[2,6-ⁱPr₂C₆H₃)N=C(H)C₆H₄O-κ¹(O)]₆U}^2?, 4. While 2 shows normal κ²-coordination through both oxygen and nitrogen donors, 3 has two salicylaldiminate ligands bound only through oxygen and 4 has all six ligands bound only through oxygen. This is an exceedingly rare example of a chelating ligand not completing its chelation in f-element chemistry. In addition, 4 is the first report of a homoleptic octahedral actinide complex with a Schiff base ligand.     

Elusive Terminal Copper Arylnitrene Intermediates

We report herein three new modes of reactivity between arylazides N₃Ar with a bulky copper(I) β-diketiminate. Addition of N₃Ar^X3 (Ar^X3=2,4,6-X₃C₆H₂; X=Cl or Me) to [ⁱPr₂NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [ⁱPr₂NN]Cu(NCMe) with bulkier azides N₃Ar leads to terminal nitrenes [ⁱPr₂NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-ⁱPr₂C₆H₃) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr₂C₆H₂). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [ⁱPr₂NN]Cu=NAr that undergo nitrene group transfer to PMe₃, ^tBuNC, and even into a benzylic sp³ C−H bond of ethylbenzene.     

Styrene polymerization with nickel complexes/methylaluminoxane catalytic system

Polymerization of styrene using β‐diketiminate nickel (II) bromide complexes CH{C(R)NAr}₂NiBr (R = CH₃, Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; R = CH₃, Ar = 2,6‐Me₂C₆H₃, 2 ; R = CF₃, Ar = 2,6‐ⁱPr₂C₆H₃, 3 ; R = CF₃, Ar = 2,6‐Me₂C₆H₃, 4 ) in the presence of methylaluminoxane was studied. Compound 3 is the most active styrene polymerization catalyst of all the nickel complexes tested. The activity of these catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. Weight‐average molecular weight of the prepared polystyrene ranges from 21 000 to 72 000, with polydispersity indexes of 1.95–2.78. The microstructure of the obtained products is atactic polystyrenes from NMR analyses. Copyright © 2008 John Wiley & Sons, Ltd.     

Direct Synthesis of Titanium Complexes with Chelating cis‐9,10‐Dihydrophenanthrenediamide Ligands through Sequential C?C Bond‐Forming Reactions from o‐Metalated Arylimines

A series of new titanium(IV) complexes with o‐metalated arylimine and/or cis‐9,10‐dihydrophenanthrenediamide ligands, [o‐C₆H₄(CH?NR)TiCl₃] (R=2,6‐iPr₂C₆H₃ ( 3 a ), 2,6‐Me₂C₆H₃ ( 3 b ), tBu ( 3 c )), [cis‐9,10‐PhenH₂(NR)₂TiCl₂] (PhenH₂=9,10‐dihydrophenanthrene; R=2,6‐iPr₂C₆H₃ ( 4 a ), 2,6‐Me₂C₆H₃ ( 4 b ), tBu ( 4 c )), [{cis‐9,10‐PhenH₂(NR)₂}{o‐C₆H₄(HC?NR)}TiCl] (R=2,6‐iPr₂C₆H₃ ( 5 a ), 2,6‐Me₂C₆H₃ ( 5 b ), tBu ( 5 c )), have been synthesised from the reactions of TiCl₄ with o‐C₆H₄(CH?NR)Li (R=2,6‐iPr₂C₆H₃, 2,6‐Me₂C₆H₃, tBu). Complexes 4 and 5 were formed unexpectedly from the reactions of TiCl₄ with two or three equivalents of the corresponding o‐C₆H₄(CH?NR)Li followed by sequential intramolecular C? C bond‐forming reductive elimination and oxidative coupling reactions. Attempts to isolate the intermediates, [{o‐C₆H₄(CH?NR)}₂TiCl₂] ( 2 ), were unsuccessful. All complexes were characterised by ¹H and ¹³C NMR spectroscopy, and the molecular structures of 3 a , 4 a – c , 5 a , and 5 c were determined by X‐ray crystallography.     

Charge Effects in PCP Pincer Complexes of NiII bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis

This contribution reports on a new family of Ni^II pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands ^RPIMC^HOP^R′ react at room temperature with Ni^II precursors to give the corresponding complexes [(^RPIMCOP^R′)NiBr], where ^RPIMCOP^R=κ^P,κ^C,κ^P‐{2‐(R′₂PO),6‐(R₂PC₃H₂N₂)C₆H₃}, R=iPr, R′=iPr ( 3 b , 84 %) or Ph ( 3 c , 45 %). Selective N‐methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO₂CF₃) gave the corresponding imidazoliophosphine [(^iPrPIMIOCOP^iPr)NiBr][OTf], 4 b , in 89 % yield (^iPrPIMIOCOP^iPr=κ^P,κ^C,κ^P‐{2‐(iPr₂PO),6‐(iPr₂PC₄H₅N₂)C₆H₃}). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOP^iPr)NiBr], 5 b , in 47 % yield (NHCCOP^iPr=κ^P,κ^C,κ^C‐{2‐(iPr₂PO),6‐(C₄H₅N₂)C₆H₃)}). The bromo derivatives 3–5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [(^RPIMCOP^R)Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [(^RPIMIOCOP^R)Ni(MeCN)][OTf]₂ [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOP^R)Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b , 3 c , 5 b , 6 b , and 8 a were also subjected to X‐ray diffraction studies. The acetonitrile adducts 6 – 8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6 – 8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95.     

Synthesis and spectroscopic studies of homo- and heteroleptic N-arylsalicylaldiminates of titanium(IV), zirconium(IV) and chromium(III)

Homo- and heteroleptic N-arylsalicylaldiminate derivatives of Ti^IV and Zr^IV of the type, MX_4–x (OC₆H₄CH=NAr) _x (X = OPrⁱ, x = 2,3; X = Cl, x = 1,2,3,4; Ar = C₆H₃Me₂-2,6, C₆H₃Et₂-2,6) have been prepared by reactions in the desired molar ratios of: (i) Ti(OPrⁱ)₄/Zr(OPrⁱ)₄·PrⁱOH with N-arylsalicylaldimines in benzene, and (ii) MCl₄ (M = Ti, Zr) with Me₃SiOC₆H₄CH=NAr or HOC₆H₄CH=NAr in the presence of Et₃N as a base or the potassium salt of N-arylsalicylaldimines in benzene. The three homoleptic derivatives of Cr^III, Cr(OC₆H₄CH=NAr)₃ (Ar = C₆H₂Me₃-2,4,6, C₆H₃Et₂-2,6, C₆H₃Prⁱ ₂-2,6) have also been prepared by salt-elimination. All of these new derivatives have been characterized by elemental analyses, spectroscopic [i.r., ¹H and ¹³C-n.m.r. (Ti and Zr complexes), and electronic (for Cr complexes)] studies, as well as molecular weight measurements.     

Die Struktur von [Li(tmeda)2][Zn(2,4,6-i-Pr3C6H2)3]

X-Ray Structure of [Li(tmeda)₂][Zn(2,4,6- i Pr₃C₆H₂)₃] A side reaction of zinc halide containing VCl₂(tmeda)₂ and Li(2,4,6-iPr₃C₆H₂) formed [Li(tmeda)₂][Zn(2,4,6-iPr₃C₆H₂)₃] · 0,5[(tmeda)Li(μ-Cl)]₂. The crystal structure (orthorhombic, Pbca, a = 26,226(2), b = 19,739(2), c = 27,223(5) Å, Z = 8, R = 0,062, wR² = 0,154) contains trigonal planar zinc anions with Zn–C distances of 2,039(7) Å (average) and a propeller like arrangement of the aryl rings.     

Vinyl polymerization of norbornene by mono‐ and trinuclear nickel complexes with indanimine ligands

A series of new indanimine ligands [ArN?CC₂H₃(CH₃)C₆H₂(R)OH] (Ar = Ph, R = Me ( 1 ), R = H ( 2 ), and R = Cl ( 3 ); Ar = 2,6‐i‐Pr₂C₆H₃, R = Me ( 4 ), R = H ( 5 ), and R = Cl ( 6 )) were synthesized and characterized. Reaction of indanimines with Ni(OAc)₂·4H₂O results in the formation of the trinuclear hexa(indaniminato)tri (nickel(II)) complexes Ni₃[ArN = CC₂H₃(CH₃)C₆H₂(R)O]₆ (Ar = Ph, R = Me ( 7 ), R = H ( 8 ), and R = Cl ( 9 )) and the mononuclear bis(indaniminato)nickel (II) complexes Ni[ArN?CC₂H₃(CH₃)C₆H₂(R)O]₂ (Ar = 2,6‐i‐Pr₂C₆H₃, R = Me ( 10 ), R = H ( 11 ), and R = Cl ( 12 )). All nickel complexes were characterized by their IR, NMR spectra, and elemental analyses. In addition, X‐ray structure analyses were performed for complexes 7 , 10 , 11 , and 12 . After being activated with methylaluminoxane (MAO), these nickel(II) complexes can polymerize norbornene to produce addition‐type polynorbornene (PNB) with high molecular weight M_v (10⁶ g mol^?1), highly catalytic activities up to 2.18 × 10⁷ gPNB mol^?1 Ni h^?1. Catalytic activities and the molecular weight of PNB have been investigated for various reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 489–500, 2008     

An H-Substituted Rhodium Silylene

Divergent reactivity of organometallic rhodium(I) complexes, which led to the isolation of neutral rhodium silylenes, is described. Addition of PhRSiH₂ (R=H, Ph) to the rhodium cyclooctene complex (^iPrNNN)Rh(COE) (1-COE; ^iPrNNN=2,5-[iPr₂P=N(4-iPrC₆H₄)]₂N(C₆H₂)⁻, COE=cyclooctene) resulted in the oxidative addition of an Si−H bond, providing rhodium(III) silyl hydride complexes (^iPrNNN)Rh(H)SiHRPh (R=H, 2 -SiH₂Ph; Ph, 2 -SiHPh₂). When the carbonyl complex (^iPrNNN)Rh(CO) ( 1 -CO) was treated with hydrosilanes, base-stabilized rhodium(I) silylenes κ²-N,N-(^iPrNNN)(CO)Rh=SiRPh (R=H, 3 -SiHPh; Ph, 3 -SiPh₂) were isolated and characterized using multinuclear NMR spectroscopy and X-ray crystallography. Both silylene species feature short Rh−Si bonds [2.262(1) Å, 3 -SiHPh; 2.2702(7) Å, 3 -SiPh₂] that agree well with the DFT-computed structures. The overall reaction led to a change in the ^iPrNNN ligand bonding mode (κ³→κ²) and loss of H₂ from PhSiRH₂, as corroborated by deuterium labelling experiments.     

Ethylene/1-hexene copolymerization by salicylaldiminato vanadium(III) complexes activated with diethylaluminum chloride

Mono salicylaldiminato vanadium（Ⅲ） complexes（1a-1f）[RN = CH（ArO）]VCl₂（THF）₂（Ar = C₆H₄（1a-1e）,R = Ph,1a;R = p-CF₃Ph,1b;R = 2,6-Me₂Ph,1c;R = 2,6-iPr₂Ph,1d;R = cyclohexyl,1e;Ar = C₆H₂tBu₂（2,4）,R = 2,6-iPr₂Ph, 1f） and bis（salicylaldiminato） vanadium（Ⅲ） complexes（2a-2f）[RN = CH（ArO）]₂VCl（THF）_x（Ar = C₆H₄（2a-2e）,x = 1 （2a-2e）,R = Ph,2a;R =p-CF₃Ph,2b;R = 2,6-Me₂Ph,2c;R = 2,6-iPr₂Ph,2d;R = cyclohexyl,2e;Ar = C₆H₂tBu₂（2,4）,R = 2,6-iPr₂Ph,x = 0,2f） have been evaluated as the active catalysts for ethylene/1-hexene copolymerization in the presence of Et₂AlCl.The ligand substitution pattern and the catalyst structure model significantly influenced the polymerization behaviors such as the catalytic activity,the molecular weight and molecular weight distribution of the copolymers etc.The highest catalytic activity of 8.82 kg PE/（mmol_V·h） was observed for vanadium catalyst 2d with two 2,6-diisopropylphenyl substituted salicylaldiminato ligands.The copolymer with the highest molecular weight was obtained by using mono salicylaldiminato vanadium catalyst 1f having ligands with tert-butyl at the ortho and para of the aryloxy moiety.     

Sterically Crowded Terphenylselenium Compounds

Extremely bulky terphenyltriselanes RSeSeSeR with R = 2,6‐(2,4,6‐Me₃C₆H₂)₂C₆H₃ and 2,6‐(2,4,6‐iPr₃C₆H₂)₂C₆H₃ were prepared. The chlorination with sulfuryl chloride resulted in the formation of the corresponding selenenyl chlorides RSeCl. In the case of the methyl substituted derivative, also a chlorination of the mesityl groups was observed and the derivative could be isolated. The molecular structure of the isopropyl substituted triselane [2,6‐(2,4,6‐iPr₃C₆H₂)₂C₆H₃Se]₂Se and that of 2,6‐(2,4,6‐Me₃C₆Cl₂)₂C₆H₃SeCl, have been determined by X‐Ray diffraction.     

Neue Aminometallane des Aluminiums und Galliums

New Aminometalanes of Aluminum and Gallium The reaction of secondary amines R′RNH with trimethyaluminum leads to the formation of dimeric aminoalanes [RR′NAlMe₂]₂ ( 1 ) (R = 2,6-Me₂C₆H₃, R′ = SiMe₂(2,4,6-Me₃C₆H₂)) and 2 (R = Ph, R′ = SiMe₃). Using a different stoichiometric ratio, a monomeric aminoalane [RR′N]₂AlMe ( 3 ) (R = Ph, R′ = SiPh₂Me) is obtained, having an aluminum atom of coordination number three due to the steric demand of the substituents. The synthesis of the corresponding aminogallanes 4 , 5 and 6 is achieved by reaction of lithium amides LiNRR′ (R = Ph, 2,6-iPr₂C₆H₃; R′ = SiMe₃, SiMe₂iPr) with dimethylgalliumchloride, Me₂GaCl, in n-hexane. The formation of the dimeric species is in 1 through carbon while that in 2 and 3 is formed through nitrogen. The X-ray single crystal structure analysis of 1 , 2 , 3 and 4 are reported.     

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ²‐HC(N‐2,6‐ⁱPr₂C₆H₃)(N‐2,6‐R₂C₆H₃)}]₂ (R=iPr ( 1 ), Me ( 7 )) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5‐trisubstituted benzenes. During the catalysis, the ultrashort Cr−Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ‐η⁶:η⁶‐1,3,5‐(Me₃Si)₃C₆H₃)[Cr{κ²‐HC(N ‐2,6‐ⁱPr₂C₆H₃)(N ‐2,6‐R₂C₆H₃)}]₂ (R=ⁱPr ( 5 ), Me ( 8 )). In the presence of σ donors, such as THF and 2,4,6‐Me₃C₆H₂CN, the bridging arene 1,3,5‐(Me₃Si)₃C₆H₃ in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes.     

Bis(β‐diketiminato) lanthanide amides: synthesis,structure and catalysis for the polymerization of l‐lactide and ε‐caprolactone

Treatment of the chlorides (L^2,6‐iPr2_Ph)₂LnCl (L^2,6‐iPr2_Ph = [(2,6‐ⁱPr₂C₆H₃)NC(Me)CHC(Me)N(C₆H₅)]^?) with 1 equiv. of NaNH(2,6‐ⁱPr₂C₆H₃) afforded the monoamides (L^2,6‐iPr2_Ph)₂LnNH(2,6‐ⁱPr₂C₆H₃) (Ln = Y ( 1 ), Yb ( 2 )) in good yields. Anhydrous LnCl₃ reacted with 2 equiv. of NaL^2,6‐iPr2_Ph in THF, followed by treatment with 1 equiv. of NaNH(2,6‐ⁱPr₂C₆H₃), giving the analogues (L^2,6‐iPr2_Ph)₂LnNH(2,6‐ⁱPr₂C₆H₃) (Ln = Sm ( 3 ), Nd ( 4 )). Two monoamido complexes stabilized by two L^2‐Me ligands, (L^2‐Me)₂LnNH(2,6‐ⁱPr₂C₆H₃) (L^2‐Me = [N(2‐MeC₆H₄)C(Me)]₂CH)^?; Ln = Y ( 5 ), Yb ( 6 )), were also synthesized by the latter route. Complexes 1 , 2 , 3 , 4 , 5 , 6 were fully characterized, including X‐ray crystal structure analyses. Complexes 1 , 2 , 3 , 4 , 5 , 6 are isostructural. The central metal in each complex is ligated by two β‐diketiminato ligands and one amido group in a distorted trigonal bipyramid. All the complexes were found to be highly active in the ring‐opening polymerization of L‐lactide (L‐LA) and ε‐caprolactone (ε‐CL) to give polymers with relatively narrow molar mass distributions. The activity depends on both the central metal and the ligand (Yb < Y < Sm ≈ Nd and L^2‐Me < L^2,6‐iPr2_Ph). Remarkably, the binary 3/benzyl alcohol (BnOH) system exhibited a striking ‘immortal’ nature and proved able to quantitatively convert 5000 equiv. of L‐LA with up to 100 equiv. of BnOH per metal initiator. All the resulting PLAs showed monomodal, narrow distributions (M_w/M_n = 1.06 ? 1.08), with molar mass (M_n) decreasing proportionally with an increasing amount of BnOH. The binary 4/BnOH system also exhibited an ‘immortal’ nature in the polymerization of ε‐CL in toluene. Copyright © 2014 John Wiley & Sons, Ltd.     

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

(Arylimido)vanadium(V) complexes containing anionic ancillary donor ligands of type, V(NAr)Cl₂(L) (Ar = 2,6-Me₂C₆H₃, L = aryloxo, ketimide phenoxyimine, etc.) exhibited high catalytic activities for ethylene polymerization in the presence of Al cocatalyst; V(NAr)Cl₂(O-2,6-Me₂C₆H₃) showed the exceptionally high activities in the presence of halogenated Al alkyls such as Et₂AlCl, EtAlCl₂, etc. (Arylimido)vanadium(V)-alkylidene complexes, V(CHSiMe₃)(NAr)(L′) (L′ = N=C ^t Bu₂, O-2,6- ⁱ Pr₂C₆H₃) exhibited the remarkable catalytic activities for ring-opening metathesis polymerization of norbornene. (Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl₂[2-Ar′NCH₂(C₅H₄N)] (R = 1-adamantyl, cyclohexyl, phenyl, Ar′ = 2,6-Me₂C₆H₃, 2,6- ⁱ Pr₂C₆H₃), exhibit the remarkable activities for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity, and the electronic nature directly affects the activity.     

Vinyl polymerization of norbornene by nickel(II) complexes bearing β‐diketiminate ligands

Norbornene polymerizations were carried out using nickel(II) bromide complexes CH{C(R)NAr}₂NiBr ( 1 , R = CH₃, Ar = 2, 6 ? ⁱPr₂C₆H₃; 2 , R = CH₃, Ar = 2, 6‐Me₂C₆H₃; 3 , R = CF₃, Ar = 2, 6 ? ⁱPr₂C₆H₃; 4 , R = CF₃, Ar = 2, 6‐Me₂C₆H₃) in the presence of methylaluminoxane. Compound 3 is the most active norbornene polymerization catalyst of all the nickel complexes tested. The activity of theses catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. The resulting polynorbornenes are vinyl type by IR and NMR analyses. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of a “Masked” Terminal Nickel(II) Sulfide by Reductive Deprotection and its Reaction with Nitrous Oxide

The addition of 1 equiv of KSCPh₃ to [L^RNiCl] (L^R={(2,6‐iPr₂C₆H₃)NC(R)}₂CH; R=Me, tBu) in C₆H₆ results in the formation of [L^RNi(SCPh₃)] ( 1 : R=Me; 2 : R=tBu) in good yields. Subsequent reduction of 1 and 2 with 2 equiv of KC₈ in cold (?25 °C) Et₂O in the presence of 2 equiv of 18‐crown‐6 results in the formation of “masked” terminal Ni^II sulfides, [K(18‐crown‐6)][L^RNi(S)] ( 3 : R=Me; 4 : R=tBu), also in good yields. An X‐ray crystallographic analysis of these complexes suggests that they feature partial multiple‐bond character in their Ni? S linkages. Addition of N₂O to a toluene solution of 4 provides [K(18‐crown‐6)][L^tBuNi(SN?NO)], which features the first example of a thiohyponitrite (κ²‐[SN?NO]^2?) ligand.     

Heterobimetallische phosphanido-verbrückte Zweikern-Komplexe - Synthese von cis-rac-[(η-C5H4R)2Zr{μ-PH(2,4,6−iPr3C6H2)}2M(CO)4] (RMe,MCr,Mo; RH,MMo)

Heterobimetallic Phosphanido-bridged Dinuclear Complexes - Syntheses of cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] (R?Me, M?Cr, Mo; R?H, M?Mo) The zirconocene bisphosphanido complexes [(η-C₅H₄R)₂Zr{PH(2,4,6-ⁱPr₃C₆H₂)}₂] (R?Me, H) react with [(NBD)M(CO)₄] (NBD?norbornadiene, M?Cr, Mo) to give only one diastereomer of the phosphanido-bridged heterobimetallic dinuclear complexes cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] [R?Me, M?Cr ( 1 ), Mo ( 2 ); R?H, M?Mo ( 3 )]. However, no reaction was observed between [(η-C₅H₅)₂Zr{PH(2,4,6-^tBu₃ C₆H₂)}₂] and [Pt(PPh₃)₄]. 1—3 were characterised spectroscopically. For 1—3 , the presence of the racemic isomer was shown by NMR spectroscopy. No reaction was observed at room temperature for 3 and CS₂, (NO)BF₄, Me₃NO or PH(2,4,6-Me₃C₆H₂)₂. With Et₂AlH or PhC?CH decomposition of 3 was observed.     

Crystalline Radicals Derived from Classical N‐Heterocyclic Carbenes

One‐electron reduction of C2‐arylated 1,3‐imidazoli(ni)um salts (IPr^Ar)Br (Ar=Ph, 3 a ; 4‐DMP, 3 b ; 4‐DMP=4‐Me₂NC₆H₄) and (SIPr^Ar)I (Ar=Ph, 4 a ; 4‐Tol, 4 b ) derived from classical NHCs (IPr=:C{N(2,6‐iPr₂C₆H₃)}₂CHCH, 1 ; SIPr=:C{N(2,6‐iPr₂C₆H₃)}₂CH₂CH₂, 2 ) gave radicals [(IPr^Ar)]^. (Ar=Ph, 5 a ; 4‐DMP, 5 b ) and [(SIPr^Ar)]^. (Ar=Ph, 6 a ; 4‐Tol, 6 b ). Each of 5 a , b and 6 a , b exhibited a doublet EPR signal, a characteristic of monoradical species. The first solid‐state characterization of NHC‐derived carbon‐centered radicals 6 a , b by single‐crystal X‐ray diffraction is reported. DFT calculations indicate that the unpaired electron is mainly located at the original carbene carbon atom and stabilized by partial delocalization over the adjacent aryl group.     

Isospecific Polymerization of Methyl Methacrylate by Intramolecular Rare‐Earth Metal Based Lewis Pairs†

A series of cationic rare‐earth aryloxide complexes, i.e., [LREOAr']⁺[B(C₆F₅)₄]^– (L = CH₃C(NAr)CHC(CH₃)(NCH(R)CH₂PPh₂); RE = Y, Lu; Ar' =2,6‐tBu₂‐C₆H₃, 2,6‐(PhCMe₂)₂‐4‐Me‐C₆H₂; Ar = 2,6‐iPr₂‐C₆H₃, 2,6‐(Ph₂CH)₂‐4‐iPr‐C₆H₂; R = H, CH₃, iPr, Ph), were prepared and applied to the Lewis pair polymerization of methyl methacrylate (MMA). The stereoregularity of the resulting PMMA was significantly affected by the R substituent on the pendant arm of the tridentate NNP ligand, and was found to increase with increase in the steric hindrance of R. When using a Ph group as R, the Y complex produced a highly isotactic polymer with an mm value of 95% and a T_g of 54.6 ^oC. In contrast, the steric hindrance of the Ar and Ar' groups had no effect on the tacticity of the resulting polymer, presumably because these two substituents were situated such that they pointed outward from the cyclic intermediates. Kinetics studies demonstrated that the polymerization was a first‐order process with regard to the monomer concentration prior to catalyst deactivation. End group analysis indicated that the polymerization was accompanied by two possibly competing chain‐termination side reactions that proceeded via intramolecular backbiting cyclization.