## 1 Introduction  
The selective transformation of a functional group within a complex molecule to generate target compounds is a very important issue in organic synthesis. Although this is not a trivial task, the use of homogeneous metal catalysts allows, in many cases, to reach compounds with remarkable levels of selectivity. Indeed, the field of homogeneous catalysis is currently so widespread that, in the literature, it is difficult to find advanced syntheses not using metal catalysts at some stage [1; 2; 3]. One of the organic transformations in which metal catalysts have played a key role is the hydration of nitriles (Scheme 1),a process of great relevance in view of the broad industrial, synthetic, biological, and pharmacological applications of corresponding primary amide products [4; 5; 6]. **Scheme 1. ** The catalytic hydration of nitriles. The conversion of nitriles into amides by conventional acid/base strategies usually requires harsh conditions and remains impractical for most purposes due to yield and selectivity issues, since these classical methods are frequently unable to control the over-hydrolysis of the primary amide product [7; 8]. The use of transition metal complexes (mainly of Groups 8-12) as catalysts under neutral and mild conditions has allowed researchers to overcome these traditional barriers, and a large number of selective catalysts for the nitrile hydration process have seen the light during the last two decades [9; 10; 11; 12; 13; 14; 15]. Among them, the commercially available hydride-platinum(II) complex [PtH{(PMe2O)2H}(PMe2 OH)] **(1)**, first described by [PERSON] and [PERSON] in 1995 [16; 17], has achieved great success among organic chemists because of its outstanding activity and selectivity and its exquisite compatibility with other functional groups (Figure 1). As a matter of fact, this platinum complex has found applications in the synthesis of a huge number of natural products and biologically active molecules of elaborate structure, making it the most widely used catalyst to date for the hydration of C=N bonds. This article intends to provide a comprehensive account on the chemistry and synthetic applications of [PtH{(PMe2O)2H}(PMe2 OH)] **(1)**. The literature and patented works published up to July 2015 are covered. **2. Preparation of Complex [PtH{(PMe2O)2H}(PMe2 OH)], First Catalytic Studies and Mechanism of Action**  
The synthesis of complex [PtH{(PMe2O)2H}(PMe2 OH)] **(1)** involves the reaction of the platinum(0) precursor [Pt(PPh3)4] with an excess (five equiv.) of dimethylphosphine oxide Me2P(=O)H, which tautomerizes _in situ_ into the phosphinite ligand Me2 POH, in toluene under inert atmosphere. The reaction proceeds at room temperature, and the complex precipitates directly in the medium, thus making its isolation easy by simple filtration (isolated yields are usually in the range 75%-80%) [16; 17; 18; 19]. In their first studies, [PERSON] and [PERSON] demonstrated the ability of **1** to selectively hydrate different model nitrile substrates, such as benzonitrile, acetonitrile, acrylonitrile, or 3-cyanopyridine, employing water, aqueous ethanol, or aqueous THF as the reaction medium at 70-90 \({}^{\circ}\)C [16; 17; 18]. The remarkable activity  
Figure 1: Structure of the nitrile hydration catalyst [PtH{(PMe2O)2H}(PMe2 OH)] **(1)**. of [PtH{(PMe2O2H})(PMe2 OH)] **(1)** was readily evidenced in these seminal works, with reported turnover frequencies exceeding 1400 h\({}^{-1}\) and turnover numbers of up to 77,000. Remarkably, contrary to other metal catalysts reported in the literature, complex **1** was able to operate under neutral conditions. The studies by [PERSON] and [PERSON] also showed that the size of the substituents on the phosphorus ligand is key to achieving good catalytic activity, the performances of the related complex [PtH{(PPh2O2H})(PPh2 OH)] containing a bulkier phosphinito ligand being significantly lower in comparison to those of **1** (an additional example has been recently described [20]).