chemistry

Transition metal phosphinimide complexes

Transition metal phosphinimide complexes is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Transition metal phosphinimide complexes rather than just read about it. In short: Transition metal phosphinimide complexes are metal complexes that contain phosphinimide ligands of the general formula NPR3− (R = organic substituent). Several coordination modes have been observed, including terminal and various bridging geometries.

Key takeaways

Transition metal phosphinimide complexes belongs to chemistry; place it in that map before memorising details.
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Reference excerpt

Transition metal phosphinimide complexes are metal complexes that contain phosphinimide ligands of the general formula NPR3− (R = organic substituent). Several coordination modes have been observed, including terminal and various bridging geometries. In the terminal bonding mode the M-N=P core is usually linear but some are quite bent. The preferred coordination type varies with the oxidation state and coligands on the metal and the steric and electronic properties of the R groups on phosphorus. Many transition metal phosphinimide complexes have been well-developed and, more recently, main group phosphinimide complexes have been synthesized.

Complexes of Ti, Zr, V, Ta Complexes of Phosphinimide are generally prepared by two routes. For highly electrophilic metal chlorides, the silyl derivative is convenient since is generates volatile trimethylsilyl chloride:

R3PNSiMe3 + LnMCl → R3PN-MLn + ClSiMe3 CpTi(NPR3)Cl2 is prepared by this route. More common are salt-elimination reactions:

R3PNLi + LnMCl → R3PN-MLn + LiCl

Phosphinimide polyethylene catalysts Phosphinimide ligands have shown promise in the area of ethylene polymerization. In terms of homogeneous catalysts, this field has been dominated by metallocene-based catalysts inspired by the Kaminsky catalyst in 1976. Initially phosphinimide ligands were suggested for polyethylene synthesis due to the fact they have similar steric and electronic properties to metallocene polyethylene catalysts. In most respects the steric and electronic properties, of phosphinimides and cyclopentadienyl are comparable ligands. Metal bound t-Bu3PN− has a cone angle of 87° vs 83 for cylclopentadienyl. Compared to Cp, the bulky substituents of the phosphinimide ligand are more distant from the metal, which increase the exposure of the metal centre to substrate. The less sterically crowded metal centre appears to be particularly susceptible to deactivation however.

The precatalyst are prepared by alkylation and arylation of the phosphinimide complexes is possible through alkyllithium or Grignard reagents, giving products such as CpTi(NPR3)Me2. The zirconium complexes (R3PN)2ZrCl2 can be alkylated or arylated through simple substitution. These organoTi and organoZr complexes are activated by treatment with MAO and B(C6F5)3 as a cocatalyst to activate polymerization through methyl abstraction. The phosphinimide catalyst is thought to be homogeneous and single sited. It therefore produces reactivity comparable to metallocene catalysts which are also believed to be homogeneous, single sited catalysts. The catalytic process is assumed to proceed in much of the same way as metallocene based catalysts, as the chemistry is thought to occur primarily with the metal centre and not through the bulky ligands.

References

Illustrations

Transition metal phosphinimide complexes: The possible bonding modes of phosphinimide ligands include: bridging - linear (A) or bent (B), μ2-N-bridging – unsymmetrical (C) or symmetrical (D), and μ3-N-bridging (E). — The possible bonding modes of phosphinimide ligands include: bridging - linear (A) or bent (B), μ2-N-bridging – unsymmetrical (C) or symmetrical (D), and μ3-N-bridging (E).

Transition metal phosphinimide complexes: Cone angles of a tert-butyl phosphinimide ligands and cyclopentadienyl ligands when bonded to a metal centre — Cone angles of a tert-butyl phosphinimide ligands and cyclopentadienyl ligands when bonded to a metal centre

Worked examples

Example 1 — a first encounter with Transition metal phosphinimide complexes

Start with the simplest possible case. Write down what Transition metal phosphinimide complexes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Transition metal phosphinimide complexes before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Transition metal phosphinimide complexes ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Transition metal phosphinimide complexes

In research: Transition metal phosphinimide complexes appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Transition metal phosphinimide complexes in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Transition metal phosphinimide complexes is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coordination complexes, Transition metal compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Transition metal phosphinimide complexes outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Transition metal phosphinimide complexes in 20 minutes

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Frequently asked questions

What is Transition metal phosphinimide complexes in simple terms?

Why does Transition metal phosphinimide complexes matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Transition metal phosphinimide complexes?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Transition metal phosphinimide complexes.