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).

The benzylene-linked [PNP] scaffolds HN(CH-o-CHPPh) ([A]H) and HN(CH-o-CHPPh) ([B]H) have been used for the synthesis of zirconium and hafnium complexes. For both ligands, the dimethylamides [A]M(NMe) ([A]1-M) and [B]M(NMe) ([B]1-M) were prepared and converted to the iodides [A]MI ([A]2-M) and [B]MI ([B]2-M) (M = Zr, Hf). Starting from these iodides, the corresponding benzyl derivatives [A]MBn ([A]3-M) and [B]MBn ([B]3-M) (M = Zr, Hf) were obtained via reaction with BnMg(OEt). For zirconium, the benzylic ligand positions in [A]3-Zr and [B]3-Zr were found to cyclometalate readily, which led to the corresponding κ-[PCNP]ZrBn complexes [A]4-Zr and [B]4-Zr. As these complexes failed to hydrogenate cleanly, cyclometalated derivatives with only one alkyl substituent were targeted and the mixed benzyl chlorides κ-[PCNP]MBnCl ([B]5-M, M = Zr, Hf) were obtained in the case of ligand [B]. Upon hydrogenation of [B]5-Zr, the η-tolyl complex [B]Zr(η-CH)Cl ([B]6-Zr) was generated cleanly, but the corresponding hafnium complex [B]5-Hf was found to decompose unselectively in the presence of H. Using a closely related carbazole-based [PNP] ligand, Gade and co-workers have shown recently that zirconium η-arene complexes similar to [B]6-Zr may serve as zirconium(ii) synthons, namely when reacted with 2,6-Dipp-NC (L) or pyridine (py). Both these substrates were shown to react cleanly with [B]6-Zr, which led to the formation of the bis-isocyanide complex [B]ZrCl(L) ([B]7-Zr) and the 2,2'-bipyridine derivative [B]ZrCl(bipy) ([B]8-Zr), respectively. Upon reaction of [B]Zr(η-CH)Cl ([B]6-Zr) with NaBEtH, the cyclometalated derivative κ-[PCNP]Zr(η-CH) ([B]9-Zr) was isolated. In an attempt to synthesise terminal hydrides, complexes [A]MI ([A]2-M) were treated with KBEtH, which led to the isolation of the cyclometalated hydrido complexes κ-[PCNP]M(H)(κ-EtBH) ([A]10-M; M = Zr, Hf) featuring a κ-bound triethyl borohydride moiety.

The closely related benzylene-linked diaminophosphines PhP(CHCH-o-NHPh) (AH) and PhP(CH-o-CHNHXyl) (BH with Xyl = 3,5-MeCH) were employed for the synthesis of tantalum(V) alkyls, which were then studied with respect to hydrogenolysis. In the case of AH, the tantalum trimethyl complex [Ta(A)Me] (1) and the tantalum hydrocarbyl complex [Ta(A)(CHSiMe)(η-EtC≡CEt)] (2) were prepared from the ligand's dilithium salt (A)Li(diox). Upon hydrogenolysis of 1 and 2, the formation of methane and SiMe, respectively, was observed, but well-defined tantalum hydrides could not be detected. In the case of BH, the cyclometalated species [Ta(B*)(NMe)] (3 with B* = κ-N,P,N,C-(PhP(CH-o-CHNXyl)(CH-o-CHNXyl))) was isolated and converted to the corresponding diiodo species [Ta(B*)I] (4). Treatment of 4 with LiCHSiMe resulted in the isolation of the corresponding dialkyl complex [Ta(B*)(CHSiMe)] (5), which was converted to the doubly cyclometalated monoalkyl complexes [Ta(B**)(CHSiMe)(PMe)] (6 with B** = κ-C,N,P,N,C-(PhP(CH-o-CHNXyl))) and [Ta(B**)(CHSiMe)(dmpe)] (7) via reaction with PMe and dmpe, respectively. In contrast to 5 and 6, 7 was found to react cleanly with dihydrogen to afford the corresponding terminal tantalum(V) hydride [Ta(B**)(H)(dmpe)] (8). Upon reaction of 7 with D, the deuteride [Ta(d-B**)(D)(dmpe)] (9) was obtained and found to contain deuterium atoms in the methine positions of both tantalaaziridine subunits. The partially deuterated derivatives [Ta(B**)(D)(dmpe)] (10) and [Ta(d-B**)(H)(dmpe)] (11) were generated via reaction of 8 and 9 with PhSiD and PhSiH, respectively. Prior to the addition of gaseous D or H, no H/D scrambling was observed in 10 or 11, indicating that the exchange of the methine positions proceeds via addition of D or H across the tantalaaziridine Ta-C bonds.

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The benzylene-linked triaminophosphanes P(C 6 H 4 -o-CH 2 NHXyl) 3 ([A]H 3 ) and P(CH 2 C 6 H 4 -o-NHPh) 3 ([B]H 3 ) react with (Me 2 N) 3 Mo≡N to afford the square-pyramidal nitrido complexes 1 and 2, each comprising one residual dimethylamido moiety and one uncoordinated ligand sidearm. Only the [A]-coordinated complex 1 was found to eliminate the remaining dimethylamido ligand on heating. Instead of the closed-cage molybdenum(VI) nitrido complex [A]Mo≡N, cyclometalated molybdaziridine 3 was isolated, as the syn alignment of the uncoordinated sidearm and nitrido ligand in 1 inhibits a pro- [a] 5442 [20] ]. Therefore, we decided to Scheme 2. Established routes to [NN 3 ]-coordinated molybdenum nitrido complexes.