Organometallic Chemistry

Volume 41

Ian Fairlamb, Jason M Lynam, Nathan J Patmore, Paul Elliott

• Publisher: Royal Society of Chemistry
• Year: 2017
• Print ISBN:
  9781782624165
• eBook ISBN:
  9781788012201
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Chimie

With the increase in volume, velocity and variety of information, researchers can find it difficult to keep up to date with the literature in their field. This interdisciplinary field has the potential to provide answers to problems and challenges faced in catalysis, synthetic organic chemistry and the development of therapeutic agents and new materials. Providing an invaluable volume, Organometallic Chemistry Volume 41 contains analysed, evaluated and distilled information on the latest in organometallic chemistry research including developments and applications of Lewis acidic boron reagents, masked low-coordinate main group species in synthesis and the diiron centre.

The diiron centre: Fe₂(CO)₉ and friends^†

Graeme Hogarth^a

DOI: 10.1039/9781782626923-00048

^a Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK E-mail: [email protected]

From the discovery of Fe₂(CO)₉ in 1905 to the intensive post-millennium study of dithiolate-bridged diiron complexes as biomimics of the active site of [FeFe]-hydrogenases, over the past century the diiron centre has been the most studied of binuclear systems. In this chapter we will focus on the synthesis, structure, bonding and reactivity of Fe₂(CO)₉, and derivatives based on the replacement or removal of one or more of the bridging carbonyl ligands.

1 Introduction

The beginning of modern organometallic chemistry is widely associated with the discovery of ferrocene^1,2 and subsequent developments leading to Wilkinson and Fischer being awarded the Nobel Prize for Chemistry in 1973. Yet, some 60 years earlier, it was the pioneering work of Mond (a German chemist who took British nationality) on the discovery and development of metal carbonyl chemistry that laid the ground work for the birth of transition metal organometallic chemistry. In 1890 Mond discovered that direct reaction of nickel and carbon monoxide afforded nickel tetracarbonyl³ and the reversible nature of this transformation was soon developed into a process for the deposition of pure nickel. A year later Mond prepared iron pentacarbonyl⁴ and began investigating its chemistry.⁵ In 1905, Dewar and Jones working at the University of Cambridge⁶ reported to the Royal Society their preliminary findings on the properties and chemistry of this “remarkable substance” noting that the yellow liquid is “rapidly decomposed by light, giving rise to a solid product and carbon monoxide”. Mond had made a similar observation and concluded that the solid was Fe₂(CO)₇.⁵ Dewar and Jones noted that “In the laboratory on bright days in February the decomposition was extremely slow, but on the same days in direct sunlight the decomposition was extremely rapid”. They analysed the volume of carbon monoxide released, their findings being consistent with one mole of CO being formed for every two moles of Fe(CO)₅ and thus concluded that the solid was Fe₂(CO)₉ (1) (Fig. 1a) and not the heptacarbonyl. They were able to isolate it as “large hexagonal plates, often 3 or 4 mm in breadth, but always rather thin”. They found the solid to be insoluble in most organic solvents but “slightly soluble in methyal, alcohol and acetone, and much more soluble in pyridine to form a reddish solution”. In 1907, Dewar and Jones reported a continuation of these studies,⁷ showing amongst other things that CO loss was reversible and when heated a new green iron carbonyl, now known to be Fe₃(CO)₁₂, was generated.

Fig. 1 Line drawings of (a) Fe₂(CO)₉, (b) the active site of [FeFe]-hydrogenase, (c) Fe₂(CO)₆(μ-S₂).

It was not until 1927 that Speyer and Wolf reported a reliable synthesis of Fe₂(CO)₉⁸ based upon the photolysis by sunlight of Fe(CO)₅ in glacial acetic acid, the displaced CO being removed upon purging periodically with hydrogen. This is close to the widely adopted synthesis today,^9,10 although hydrogen is no longer recommended to facilitate CO loss! The heavier homologues Ru₂(CO)₉ and Os₂(CO)₉ are also be prepared upon UV irradiation of the corresponding pentacarbonyls at low temperatures^11,12 and while Ru₂(CO)₉ is unstable at room temperature, Os₂(CO)₉ is an orange-yellow solid which melts without decomposition at 64–67 °C.¹¹

For around 60 years Fe₂(CO)₉ has been commercially available and this has led to its wide scale use as a convenient entry into organometallic iron chemistry.¹³ In this chapter we will look focus on the synthesis, structure, bonding and reactivity of Fe₂(CO)₉ and a wide range of derivatives formed upon replacement of one or more of the carbonyls. The diiron centre is unquestionably the most widely studied of binuclear organometallic systems and over the past 20 years the area has seen a renaissance with the realisation that the active site of [FeFe]-hydrogenases (Fig. 1b) contains a pair of iron atoms held in close proximity being supported by carbonyl, cyanide and dithiolate ligands. These enzymes are believed to be some 4 billion years old and the simple disulfide complex Fe₂(CO)₆(μ-S₂) (Fig. 1c) has been proposed as a key bridge between the mineral world and life forms developed on earth,^14–17 providing clear relevance to the continuing study of the diiron centre.

2 Fe₂(CO)₉: structure

Until the 1930s the nature of Fe₂(CO)₉ was poorly understood, with various unusual structures being proposed. In 1939, Powell and Ewens reported a single crystal X-ray analysis¹⁸ revealing D_3h symmetry and the now familiar structure with each ir...

Table of contents

• Cover
• Title
• Copyright
• Preface
• Contents
• Abbreviations
• Recent developments and applications of Lewis acidic boron reagents
• Masked low-coordinate main group species in synthesis
• The diiron centre: Fe2(CO)9 and friends1
• Taddol and Binol-derived chiral phosphonites in asymmetric catalysis
• Gold-catalysed C–F bond activation
• Silylamides: towards a half-century of stabilising remarkable f-element chemistry