science

Transition metal phosphido complexes

Transition metal phosphido complexes is a science 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 phosphido complexes rather than just read about it. In short: A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P−) is comparable to an amido anion (R2N−), except that the M-P distances are longer and the phosphorus atom is more sterically accessible.

Key takeaways

Transition metal phosphido complexes belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Transition metal phosphido complexes to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Transition metal phosphido complexes from memory before moving on to harder problems.

Reference excerpt

A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P−) is comparable to an amido anion (R2N−), except that the M-P distances are longer and the phosphorus atom is more sterically accessible. For these reasons, phosphido is often a bridging ligand. The -PH2 ion or ligand is also called phosphanide or phosphido ligand.

Synthesis One can generate transition-metal phosphido complexes by direct activation of P-H bonds, as mostly seen in the late-transition-metal complexes. For example, the reaction of Vaska's complex analogs with the parent phosphine generate the following transition-metal phosphido complex.

Alkali metal phosphides sometimes reduce the metal center.

The alternative salt metathesis route involves the reaction of alkali metal diorganophosphides with metal halides. A typical phosphide reagent is lithium diphenylphosphide.

Structure

Most complexes of the phosphide ligand can be classified into one of three structural classes:

those where the phosphide is a terminal ligand and phosphorus is pyramidal, those where the phosphide is a terminal ligand and phosphorus is planar, those where the phosphide is a bridging ligand and phosphorus is tetrahedral.

Pyramidal terminal phosphido ligands

In most complexes with terminal phosphido ligands, phosphorus is pyramidal, as expected with a stereochemically active lone pair of electrons. The M-P bond length in the pyramidal phosphide complex is longer than the M-P bond length in corresponding transition metal phosphine complexes. The pyramidal phosphido complex. In the complex, the Os-PHPh bond is 0.11 Å longer than the Os-PPh3 and the Os-P-C angle is 113o. The elongated Os-PHPh bond is often attributed to the electronic repulsion of the lone pair and nonbonding electrons on Os. Also, in another ruthenium complex, the Ru-P(Me)Ph bond is 0.17 Å longer than Ru-PH(Me)Ph in the related phosphine ligand version of the complex, [(dmpe)2Ru(H)PH(Me)Ph]+. Additionally electronic repulsion of the P-centered lone pair and metal-based electrons enhance the nucleophilicity of the phosphide ligand. This high basicity and high nucleophilicity leads to the dimerization reaction. The inversion of configuration at pyramidal terminal phosphides has been observed by 31P NMR spectroscopy.

Planar terminal phosphido ligands

Planar terminal phosphido ligands are also known. Terminal planar phosphido ligands engage in M-P multiple bonding. Planar phosphido complexes usually have shorter M-P bonds and wider M-P-R angles. In the tungsten complex, the W-PHPh bond is 0.26 Å shorter than W-PEt3 bond in the same complex, and the W-P-C angle is 140°. In (C5H5)2Hf(PR2)2, which can be prepared by salt metathesis from hafnocene dichloride, Hf(IV) is bonded to both planar and pyramidal phosphido ligands. These ligand types interconvert on the NMR timescale corresponding to an activation energy of about 8 kcal/mol. According to X-ray crystallography, the Hf-P distances are 2.488 (planar P) and 2.682 Å (pyramidal P).

Bridging phosphido ligands

In most of its complexes, the phosphido ligand is a bridging ligand. No lone pairs remain on phosphorus. These complexes have the formula [M(μ-PR2)Ln]2. One example is [Fe(μ-PPh2)(CO)3]2. Phosphido ligands are often installed by salt metathesis reactions. Sources of R2P+ and R2P− are provided by phosphorus halides and alkali metal phosphides respectively. Illustrative of the use of R2PCl-like reagents is the synthesis of a diiron diphosphide:

Na2Fe2(CO)8 + 2 Ph2PCl → Fe2(PPh2)2(CO)6 + 2 NaCl + 2 CO

Role in catalysis

Metal phosphido complexes are intermediates the catalytic hydrophosphinations, which is a route to organophosphorus compound. Although this methodology has not proven to be of practical value, it offers the potential for producing specialized phosphine ligands. In one case, a Pt(0) catalyst undergoes oxidative addition of a secondary phosphine to form the corresponding Pt(II) phosphido complex, which react with electrophilic alkenes such as acrylonitrile. This P-C bond forming step proceeds through an outer-sphere, Michael-type addition. cAlkene insertion into the metal-hydrogen bond is also invoked in some hydrophosphinations. Metal phosphides have been used in the synthesis of P-stereogenic phosphines by exploiting the high nucleophilicity in the pyramidal phosphide complex.

References

Illustrations

Worked examples

Example 1 — a first encounter with Transition metal phosphido complexes

Start with the simplest possible case. Write down what Transition metal phosphido complexes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 phosphido 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 phosphido 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 phosphido complexes

In research: Transition metal phosphido complexes appears in science 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 phosphido 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 phosphido complexes is common in secondary-school and first-year university syllabi. It links to neighbouring topics Phosphides, so understanding it makes those chapters shorter.
In everyday life: Look for Transition metal phosphido 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Transition metal phosphido complexes” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Transition metal phosphido complexes in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Transition metal phosphido complexes means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Transition metal phosphido complexes out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Transition metal phosphido complexes in simple terms?

Why does Transition metal phosphido complexes matter?

Because it connects several science 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 phosphido 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 phosphido complexes.