The N,N′,N″-triphenyl-substituted derivative of tris(2-aminoethyl)phosphine (Ph 3 -phospha-tren, P-(CH 2 CH 2 NHR) 3 , R = Ph) and four derivatives of the related t r i s ( 3 -a m i n o p r o p y l ) p h o s p h i n e ( p h o s p h at r p n , P-(CH 2 CH 2 CH 2 NHR) 3 , R = i Pr, t Bu, Si t BuMe 2 , Ph) have been synthesized in addition to the parent phospha-trpn. Out of these ligand systems, only the N,N′,N″-triphenyl-substituted phosphatrpn derivative P(CH 2 CH 2 CH 2 NHPh) 3 was found to be suitable for coordination to group 4 metals. For titanium, zirconium, and hafnium, the C 3 -symmetric endo-P-configured dimethylamido complexes Ph [PN 3 ]M(NMe 2 ) of the former ligand have been prepared and converted into the corresponding triflates Ph [PN 3 ]M(OTf). Starting from these triflates, the benzyl complexes Ph [PN 3 ]M(Bn) (M = Ti, Zr, Hf) have been obtained via reaction with Bn 2 Mg(THF) 2 . In case of titanium, the benzyl species Ph [PN 3 ]Ti(Bn) is prone to thermal elimination of toluene, which results in the formation of a cyclometalated species. These findings are discussed in context with the very few group 4 trisamidophosphine complexes that have been reported earlier.
The closely related benzylene-linked diaminophosphines PhP(CH 2 C 6 H 4 -o-NHPh) 2 ([ Ph A]H 2 ) and PhP-(C 6 H 4 -o-CH 2 NHXyl) 2 ([B]H 2 ) were prepared as robust alternatives to the previously reported N,N′-bis(trimethylsilyl)-substituted derivative PhP(CH 2 C 6 H 4 -o-NHSiMe 3 ) 2 ([ Si A]H 2 ). Upon reaction of [ Ph A]H 2 and [B]H 2 with M(NMe 2 ) 4 (M = Zr, Hf), the respective dimethylamido complexes [ Ph A]M(NMe 2 ) 2 and [B]M(NMe 2 ) 2 ([ Ph A]-1-M and [B]-1-M, M = Zr, Hf) were isolated in high yields and converted to the corresponding diiodo derivatives [ Ph A]MI 2 and [B]MI 2 ([ Ph A]-2-M and [B]-2-M, M = Zr, Hf). In contrast to [ Si A]ZrI 2 , these thermally robust diiodo complexes were found to react cleanly with Bn 2 MgL 2 (L = THF or Et 2 O), resulting in the corresponding dibenzyl species [ Ph A]MBn 2 and [B]MBn 2 ([ Ph A]-4-M and [B]-4-M, M = Zr, Hf). Upon addition of [B]H 2 to [B]ZrBn 2 , the related homoleptic species [B] 2 Zr ([B]-5-Zr) was generated. Similar 2:1 complexes have not been observed for the hafnium homologue bearing the latter ligand or for [ Si A]-or [ Ph A]-coordinated complexes. The former dibenzyl complexes were reacted with 2,6-xylylisonitrile, and clean conversions to the bis-η 2 -iminoacyl complexes [B]-6-Hf and [ Ph A]-6-M were observed for [B]-4-Hf and [ Ph A]-4-M (M = Zr, Hf). For [ Si A]HfBn 2 ([ Si A]-4-Hf) only one equivalent of the former isonitrile was inserted into one of the hafnium carbon bonds, which is in line with the steric differences between [ Si A] and [ Ph A].
The coordination chemistry of the phosphine-tethered diamidophosphine ligands PhP(CH2CH2CH2NHPh)2 (pr[NPN]H2) and PhP(1,2-CH2-C6H4-NHSiMe3)2 (bn[NPN]H2) featuring six-membered N–C3–P chelates was explored with group 4 metals, which allowed for the consecutive development of a new trimethylene-methane-tethered [PN2] scaffold. In the case of the propylene-linked system pr[NPN]H2, access to the sparingly soluble dibenzyl derivative pr[NPN]ZrBn2 (3-Zr) was gained, while thermally sensitive zirconium and hafnium diiodo complexes bn[NPN]MI2 (5-M, M = Zr, Hf) were isolated in the case of the benzylene-linked derivative bn[NPN]H2. Despite the related phosphine-tethered backbone architectures of both of these ligands, their group 4 complexes were found to exhibit either C1-symmetric (bn[NPN]MX2) or averaged CS-symmetric (pr[NPN]MX2) structures in solution. To restrain the overall flexibility of these systems and thereby control the properties of the resulting complexes without disrupting the six-membered chelates, the new trimethylene-methane-tethered N,N′-di-(tert-butyl)-substituted [PN2]H2 protioligand was designed. This tripodal ligand system was prepared on a gram scale and its CS-symmetric dichloro complexes [PN2]MCl2 (6-M, M = Ti, Zr, Hf) were isolated subsequently. The benzene-soluble dibenzyl derivative [PN2]ZrBn2 (7-Zr) was synthesised as well and characterised by X-ray diffraction. These results are discussed not only in conjunction with the known [NPN]-coordinated group 4 complexes incorporating five-membered chelates, but also in the context of “molecular claws” that are related to the new [PN2] tripod.
A new tripodal trisamidophosphine ligand (1) based on the trisbenzylphosphine backbone has been synthesized in three steps starting from NaPH2 and phthaloyl-protected 2-aminobenzyl bromide. At elevated temperatures, 1 reacts directly with M(NMe2)4 (M = Zr, Hf) to afford the dimethylamido complexes [PN3]M(NMe2) (M = Zr, Hf) (2), which are easily converted into the corresponding triflates [PN3]MOTf (M = Zr, Hf) (3) via reaction with triethylsilyl trifluoromethanesulfonate. The related titanium chloro complex [PN3]TiCl (4-Ti) is obtained from 1 and Bn3TiCl via protonolysis. Triple deprotonation of 1 with n-butyllithium affords the tris-lithium salt Li3[PN3] (1-Li), which serves as a common starting material for the preparation of all the group(IV) chlorides [PN3]MCl (M = Ti, Zr, Hf) (4). Upon treatment of 4-Ti with Bn2Mg(thf)2, formation of a benzyltitanium species is observed, which is converted cleanly into a ligand-CH-activated species (5-Ti).
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